1.
Oxide minerals
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The oxide mineral class includes those minerals in which the oxide anion is bonded to one or more metal ions. The hydroxide bearing minerals are typically included in the oxide class, the minerals with complex anion groups such as the silicates, sulfates, carbonates and phosphates are classed separately. This list uses it to modify the Classification of Nickel–Strunz,00 Clinobirnessite*,00 Kleberite*,00 Chubutite*,00 Struverite
2.
Chemical formula
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These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas can fully specify the structure of only the simplest of molecules and chemical substances, the simplest types of chemical formulas are called empirical formulas, which use letters and numbers indicating the numerical proportions of atoms of each type. Molecular formulas indicate the numbers of each type of atom in a molecule. For example, the formula for glucose is CH2O, while its molecular formula is C6H12O6. This is possible if the relevant bonding is easy to show in one dimension, an example is the condensed molecular/chemical formula for ethanol, which is CH3-CH2-OH or CH3CH2OH. For reasons of structural complexity, there is no condensed chemical formula that specifies glucose, chemical formulas may be used in chemical equations to describe chemical reactions and other chemical transformations, such as the dissolving of ionic compounds into solution. A chemical formula identifies each constituent element by its chemical symbol, in empirical formulas, these proportions begin with a key element and then assign numbers of atoms of the other elements in the compound, as ratios to the key element. For molecular compounds, these numbers can all be expressed as whole numbers. For example, the formula of ethanol may be written C2H6O because the molecules of ethanol all contain two carbon atoms, six hydrogen atoms, and one oxygen atom. Some types of compounds, however, cannot be written with entirely whole-number empirical formulas. An example is boron carbide, whose formula of CBn is a variable non-whole number ratio with n ranging from over 4 to more than 6.5. When the chemical compound of the consists of simple molecules. These types of formulas are known as molecular formulas and condensed formulas. A molecular formula enumerates the number of atoms to reflect those in the molecule, so that the formula for glucose is C6H12O6 rather than the glucose empirical formula. However, except for very simple substances, molecular chemical formulas lack needed structural information, for simple molecules, a condensed formula is a type of chemical formula that may fully imply a correct structural formula. For example, ethanol may be represented by the chemical formula CH3CH2OH
3.
Crystal system
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In crystallography, the terms crystal system, crystal family and lattice system each refer to one of several classes of space groups, lattices, point groups or crystals. Informally, two crystals are in the crystal system if they have similar symmetries, though there are many exceptions to this. Space groups and crystals are divided into seven crystal systems according to their point groups, five of the crystal systems are essentially the same as five of the lattice systems, but the hexagonal and trigonal crystal systems differ from the hexagonal and rhombohedral lattice systems. The six crystal families are formed by combining the hexagonal and trigonal crystal systems into one hexagonal family, a lattice system is a class of lattices with the same set of lattice point groups, which are subgroups of the arithmetic crystal classes. The 14 Bravais lattices are grouped into seven lattice systems, triclinic, monoclinic, orthorhombic, tetragonal, rhombohedral, hexagonal, in a crystal system, a set of point groups and their corresponding space groups are assigned to a lattice system. Of the 32 point groups that exist in three dimensions, most are assigned to only one system, in which case both the crystal and lattice systems have the same name. However, five point groups are assigned to two systems, rhombohedral and hexagonal, because both exhibit threefold rotational symmetry. These point groups are assigned to the crystal system. In total there are seven crystal systems, triclinic, monoclinic, orthorhombic, tetragonal, trigonal, hexagonal, a crystal family is determined by lattices and point groups. It is formed by combining crystal systems which have space groups assigned to a lattice system. In three dimensions, the families and systems are identical, except the hexagonal and trigonal crystal systems. In total there are six families, triclinic, monoclinic, orthorhombic, tetragonal, hexagonal. Spaces with less than three dimensions have the number of crystal systems, crystal families and lattice systems. In one-dimensional space, there is one crystal system, in 2D space, there are four crystal systems, oblique, rectangular, square and hexagonal. The relation between three-dimensional crystal families, crystal systems and lattice systems is shown in the table, Note. To avoid confusion of terminology, the term trigonal lattice is not used, if the original structure and inverted structure are identical, then the structure is centrosymmetric. Still, even for non-centrosymmetric case, inverted structure in some cases can be rotated to align with the original structure and this is the case of non-centrosymmetric achiral structure. If the inverted structure cannot be rotated to align with the structure, then the structure is chiral
4.
Hexagonal crystal family
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In crystallography, the hexagonal crystal family is one of the 6 crystal families. In the hexagonal family, the crystal is described by a right rhombic prism unit cell with two equal axes, an included angle of 120° and a height perpendicular to the two base axes. There are 52 space groups associated with it, which are exactly those whose Bravais lattice is either hexagonal or rhombohedral, the hexagonal crystal family consists of two lattice systems, hexagonal and rhombohedral. Each lattice system consists of one Bravais lattice, hence, there are 3 lattice points per unit cell in total and the lattice is non-primitive. The Bravais lattices in the hexagonal crystal family can also be described by rhombohedral axes, the unit cell is a rhombohedron. This is a cell with parameters a = b = c, α = β = γ ≠ 90°. In practice, the description is more commonly used because it is easier to deal with a coordinate system with two 90° angles. However, the axes are often shown in textbooks because this cell reveals 3m symmetry of crystal lattice. However, such a description is rarely used, the hexagonal crystal family consists of two crystal systems, trigonal and hexagonal. A crystal system is a set of point groups in which the point groups themselves, the trigonal crystal system consists of the 5 point groups that have a single three-fold rotation axis. The crystal structures of alpha-quartz in the example are described by two of those 18 space groups associated with the hexagonal lattice system. The hexagonal crystal system consists of the seven point groups such that all their groups have the hexagonal lattice as underlying lattice. Graphite is an example of a crystal that crystallizes in the crystal system. Note that the atom in the center of the HCP unit cell in the hexagonal lattice system does not appear in the unit cell of the hexagonal lattice. It is part of the two atom motif associated with each point in the underlying lattice. The trigonal crystal system is the crystal system whose point groups have more than one lattice system associated with their space groups. The 5 point groups in this system are listed below, with their international number and notation, their space groups in name. The point groups in this system are listed below, followed by their representations in Hermann–Mauguin or international notation and Schoenflies notation
5.
Crystallographic point group
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For a periodic crystal, the group must also be consistent with maintenance of the three-dimensional translational symmetry that defines crystallinity. The macroscopic properties of a crystal would look exactly the same before, in the classification of crystals, each point group is also known as a crystal class. There are infinitely many three-dimensional point groups, however, the crystallographic restriction of the infinite families of general point groups results in there being only 32 crystallographic point groups. These 32 point groups are one-and-the same as the 32 types of morphological crystalline symmetries derived in 1830 by Johann Friedrich Christian Hessel from a consideration of observed crystal forms, the point groups are denoted by their component symmetries. There are a few standard notations used by crystallographers, mineralogists, for the correspondence of the two systems below, see crystal system. In Schoenflies notation, point groups are denoted by a symbol with a subscript. The symbols used in crystallography mean the following, Cn indicates that the group has a rotation axis. Cnh is Cn with the addition of a plane perpendicular to the axis of rotation. Cnv is Cn with the addition of n mirror planes parallel to the axis of rotation, s2n denotes a group that contains only a 2n-fold rotation-reflection axis. Dn indicates that the group has a rotation axis plus n twofold axes perpendicular to that axis. Dnh has, in addition, a plane perpendicular to the n-fold axis. Dnd has, in addition to the elements of Dn, mirror planes parallel to the n-fold axis, the letter T indicates that the group has the symmetry of a tetrahedron. Td includes improper rotation operations, T excludes improper rotation operations, the letter O indicates that the group has the symmetry of an octahedron, with or without improper operations. Due to the crystallographic restriction theorem, n =1,2,3,4, d4d and D6d are actually forbidden because they contain improper rotations with n=8 and 12 respectively. The 27 point groups in the table plus T, Td, Th, O, an abbreviated form of the Hermann–Mauguin notation commonly used for space groups also serves to describe crystallographic point groups. Group names are Molecular symmetry Point group Space group Point groups in three dimensions Crystal system Point-group symbols in International Tables for Crystallography,12.1, pp. 818-820 Names and symbols of the 32 crystal classes in International Tables for Crystallography. 10.1, p.794 Pictorial overview of the 32 groups Point Groups - Flow Chart Inorganic Chemistry Group Theory Practice Problems
6.
H-M symbol
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In geometry, Hermann–Mauguin notation is used to represent the symmetry elements in point groups, plane groups and space groups. It is named after the German crystallographer Carl Hermann and the French mineralogist Charles-Victor Mauguin and this notation is sometimes called international notation, because it was adopted as standard by the International Tables For Crystallography since their first edition in 1935. Rotation axes are denoted by a number n —1,2,3,4,5,6,7,8, for improper rotations, Hermann–Mauguin symbols show rotoinversion axes, unlike Schoenflies and Shubnikov notations, where the preference is given to rotation-reflection axes. The rotoinversion axes are represented by the number with a macron. The symbol for a plane is m. The direction of the plane is defined as the direction of perpendicular to the face. Hermann–Mauguin symbols show symmetrically non-equivalent axes and planes, the direction of a symmetry element is represented by its position in the Hermann–Mauguin symbol. If a rotation axis n and a mirror plane m have the same direction, if two or more axes have the same direction, the axis with higher symmetry is shown. Higher symmetry means that the axis generates a pattern with more points, for example, rotation axes 3,4,5,6,7,8 generate 3-, 4-, 5-, 6-, 7-, 8-point patterns, respectively. Improper rotation axes 3,4,5,6,7,8 generate 6-, 4-, 10-, 6-, 14-, 8-point patterns, if both, the rotation and rotoinversion axes satisfy the previous rule, the rotation axis should be chosen. For example, 3/m combination is equivalent to 6, since 6 generates 6 points, and 3 generates only 3,6 should be written instead of 3/m. Analogously, in the case when both 3 and 3 axes are present,3 should be written, however we write 4/m, not 4/m, because both 4 and 4 generate four points. Finally, the Hermann–Mauguin symbol depends on the type of the group and these groups may contain only two-fold axes, mirror planes, and inversion center. These are the point groups 1 and 1,2, m, and 2/m, and 222, 2/m2/m2/m. If the symbol contains three positions, then they denote symmetry elements in the x, y, z direction, First position — primary direction — z direction, assigned to the higher-order axis. Second position — symmetrically equivalent secondary directions, which are perpendicular to the z-axis and these can be 2, m, or 2/m. Third position — symmetrically equivalent tertiary directions, passing between secondary directions and these can be 2, m, or 2/m. These are the crystallographic groups 3,32, 3m,3, and 32/m,4,422, 4mm,4, 42m, 4/m, and 4/m2/m2/m, and 6,622, 6mm,6, 6m2, 6/m, and 6/m2/m2/m
7.
Space group
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In mathematics, physics and chemistry, a space group is the symmetry group of a configuration in space, usually in three dimensions. In three dimensions, there are 219 distinct types, or 230 if chiral copies are considered distinct, Space groups are also studied in dimensions other than 3 where they are sometimes called Bieberbach groups, and are discrete cocompact groups of isometries of an oriented Euclidean space. In crystallography, space groups are called the crystallographic or Fedorov groups. A definitive source regarding 3-dimensional space groups is the International Tables for Crystallography, in 1879 Leonhard Sohncke listed the 65 space groups whose elements preserve the orientation. More accurately, he listed 66 groups, but Fedorov and Schönflies both noticed that two of them were really the same, the space groups in 3 dimensions were first enumerated by Fedorov, and shortly afterwards were independently enumerated by Schönflies. The correct list of 230 space groups was found by 1892 during correspondence between Fedorov and Schönflies, burckhardt describes the history of the discovery of the space groups in detail. The space groups in three dimensions are made from combinations of the 32 crystallographic point groups with the 14 Bravais lattices, the combination of all these symmetry operations results in a total of 230 different space groups describing all possible crystal symmetries. The elements of the space group fixing a point of space are rotations, reflections, the identity element, the translations form a normal abelian subgroup of rank 3, called the Bravais lattice. There are 14 possible types of Bravais lattice, the quotient of the space group by the Bravais lattice is a finite group which is one of the 32 possible point groups. Translation is defined as the moves from one point to another point. A glide plane is a reflection in a plane, followed by a parallel with that plane. This is noted by a, b or c, depending on which axis the glide is along. There is also the n glide, which is a glide along the half of a diagonal of a face, and the d glide, the latter is called the diamond glide plane as it features in the diamond structure. In 17 space groups, due to the centering of the cell, the glides occur in two directions simultaneously, i. e. the same glide plane can be called b or c, a or b. For example, group Abm2 could be also called Acm2, group Ccca could be called Cccb, in 1992, it was suggested to use symbol e for such planes. The symbols for five groups have been modified, A screw axis is a rotation about an axis. These are noted by a number, n, to describe the degree of rotation, the degree of translation is then added as a subscript showing how far along the axis the translation is, as a portion of the parallel lattice vector. So,21 is a rotation followed by a translation of 1/2 of the lattice vector
8.
Crystal structure
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In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the nature of the constituent particles to form symmetric patterns that repeat along the principal directions of three-dimensional space in matter. The smallest group of particles in the material that constitutes the pattern is the unit cell of the structure. The unit cell completely defines the symmetry and structure of the crystal lattice. The repeating patterns are said to be located at the points of the Bravais lattice, the lengths of the principal axes, or edges, of the unit cell and the angles between them are the lattice constants, also called lattice parameters. The symmetry properties of the crystal are described by the concept of space groups, all possible symmetric arrangements of particles in three-dimensional space may be described by the 230 space groups. The crystal structure and symmetry play a role in determining many physical properties, such as cleavage, electronic band structure. The crystal structure of a material can be described in terms of its unit cell, the unit cell is a box containing one or more atoms arranged in three dimensions. The unit cells stacked in three-dimensional space describe the arrangement of atoms of the crystal. Commonly, atomic positions are represented in terms of fractional coordinates, the atom positions within the unit cell can be calculated through application of symmetry operations to the asymmetric unit. The asymmetric unit refers to the smallest possible occupation of space within the unit cell and this does not, however imply that the entirety of the asymmetric unit must lie within the boundaries of the unit cell. Symmetric transformations of atom positions are calculated from the group of the crystal structure. Vectors and planes in a lattice are described by the three-value Miller index notation. It uses the indices ℓ, m, and n as directional parameters, which are separated by 90°, by definition, the syntax denotes a plane that intercepts the three points a1/ℓ, a2/m, and a3/n, or some multiple thereof. That is, the Miller indices are proportional to the inverses of the intercepts of the plane with the unit cell, if one or more of the indices is zero, it means that the planes do not intersect that axis. A plane containing a coordinate axis is translated so that it no longer contains that axis before its Miller indices are determined, the Miller indices for a plane are integers with no common factors. Negative indices are indicated with horizontal bars, as in, in an orthogonal coordinate system for a cubic cell, the Miller indices of a plane are the Cartesian components of a vector normal to the plane. Likewise, the planes are geometric planes linking nodes
9.
Crystal habit
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In mineralogy, crystal habit is the characteristic external shape of an individual crystal or crystal group. A single crystals habit is a description of its shape and its crystallographic forms. Recognizing the habit may help in identifying a mineral, when the faces are well-developed due to uncrowded growth a crystal is called euhedral, one with partially developed faces is subhedral, and one with undeveloped crystal faces is called anhedral. The long axis of a quartz crystal typically has a six-sided prismatic habit with parallel opposite faces. Aggregates can be formed of individual crystals with euhedral to anhedral grains, the arrangement of crystals within the aggregate can be characteristic of certain minerals. For example, minerals used for asbestos insulation often grow in a fibrous habit, the terms used by mineralogists to report crystal habits describe the typical appearance of an ideal mineral. Recognizing the habit can aid in identification as some habits are characteristic, most minerals, however, do not display ideal habits due to conditions during crystallization. Minerals belonging to the crystal system do not necessarily exhibit the same habit. Some habits of a mineral are unique to its variety and locality, For example, while most sapphires form elongate barrel-shaped crystals, ordinarily, the latter habit is seen only in ruby. Sapphire and ruby are both varieties of the mineral, corundum. Some minerals may replace other existing minerals while preserving the originals habit, a classic example is tigers eye quartz, crocidolite asbestos replaced by silica. While quartz typically forms prismatic crystals, in tigers eye the original fibrous habit of crocidolite is preserved, the names of crystal habits are derived from, Predominant crystal faces. Abnormal grain growth Grain growth Crystallization
10.
Crystal twinning
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Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations, a twin boundary or composition surface separates the two crystals. Crystallographers classify twinned crystals by a number of twin laws and these twin laws are specific to the crystal system. The type of twinning can be a tool in mineral identification. Twinning can often be a problem in X-ray crystallography, as a crystal does not produce a simple diffraction pattern. Simple twinned crystals may be contact twins or penetration twins, contact twins share a single composition surface often appearing as mirror images across the boundary. Plagioclase, quartz, gypsum, and spinel often exhibit contact twinning, merohedral twinning occurs when the lattices of the contact twins superimpose in three dimensions, such as by relative rotation of one twin from the other. In penetration twins the individual crystals have the appearance of passing through each other in a symmetrical manner, orthoclase, staurolite, pyrite, and fluorite often show penetration twinning. If several twin crystal parts are aligned by the same twin law they are referred to as multiple or repeated twins, if these multiple twins are aligned in parallel they are called polysynthetic twins. When the multiple twins are not parallel they are cyclic twins, albite, calcite, and pyrite often show polysynthetic twinning. Closely spaced polysynthetic twinning is often observed as striations or fine lines on the crystal face. Rutile, aragonite, cerussite, and chrysoberyl often exhibit cyclic twinning, 2-normal twin, -when the twin plane and compositional plane lies noramally. 3-complex twin, -combination of parallel twinning and normal twinning on one compositional plane, there are three modes of formation of twinned crystals. Growth twins are the result of an interruption or change in the lattice during formation or growth due to a possible deformation from a larger substituting ion, deformation or gliding twins are the result of stress on the crystal after the crystal has formed. If a FCC metal like aluminum experiences extreme stresses, it will experience twinning as seen in the case of explosions, deformation twinning is a common result of regional metamorphism. Crystals that grow adjacent to each other may be aligned to resemble twinning and this parallel growth simply reduces system energy and is not twinning. Twin boundaries occur when two crystals of the same type intergrow, so only a slight misorientation exists between them. It is a highly symmetrical interface, often with one crystal the mirror image of the other, also and this is also a much lower-energy interface than the grain boundaries that form when crystals of arbitrary orientation grow together
11.
Cleavage (crystal)
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Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. Cleavage forms parallel to planes, Basal or pinacoidal cleavage occurs when there is only one cleavage plane. Mica also has basal cleavage, this is why mica can be peeled into thin sheets, cubic cleavage occurs on when there are three cleavage planes intersecting at 90 degrees. Halite has cubic cleavage, and therefore, when halite crystals are broken, octahedral cleavage occurs when there are four cleavage planes in a crystal. Octahedral cleavage is common for semiconductors, rhombohedral cleavage occurs when there are three cleavage planes intersecting at angles that are not 90 degrees. Prismatic cleavage occurs when there are two planes in a crystal. Dodecahedral cleavage occurs when there are six cleavage planes in a crystal, crystal parting occurs when minerals break along planes of structural weakness due to external stress or along twin composition planes. Parting breaks are very similar in appearance to cleavage, but only due to stress. Examples include magnetite which shows octahedral parting, the parting of corundum. Cleavage is a property traditionally used in mineral identification, both in hand specimen and microscopic examination of rock and mineral studies. As an example, the angles between the cleavage planes for the pyroxenes and the amphiboles are diagnostic. Crystal cleavage is of importance in the electronics industry and in the cutting of gemstones. Precious stones are generally cleaved by impact, as in diamond cutting, synthetic single crystals of semiconductor materials are generally sold as thin wafers which are much easier to cleave. Elemental semiconductors are diamond cubic, a group for which octahedral cleavage is observed. This means that some orientations of wafer allow near-perfect rectangles to be cleaved, most other commercial semiconductors can be made in the related zinc blende structure, with similar cleavage planes. Cleavage Mineral galleries, Mineral properties – Cleavage
12.
Fracture (mineralogy)
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In the field of mineralogy, fracture is the texture and shape of a rocks surface formed when a mineral is fractured. Minerals often have a highly distinctive fracture, making it a feature used in their identification. Fracture differs from cleavage in that the latter involves clean splitting along the planes of the minerals crystal structure. All minerals exhibit fracture, but when very strong cleavage is present, conchoidal fracture breakage that resembles the concentric ripples of a mussel shell. It often occurs in amorphous or fine-grained minerals such as flint, opal or obsidian, subconchoidal fracture is similar to conchoidal fracture, but with less significant curvature. Earthy fracture is reminiscent of freshly broken soil and it is frequently seen in relatively soft, loosely bound minerals, such as limonite, kaolinite and aluminite. Hackly fracture is jagged, sharp and not even and it occurs when metals are torn, and so is often encountered in native metals such as copper and silver. Splintery fracture comprises sharp elongated points and it is particularly seen in fibrous minerals such as chrysotile, but may also occur in non-fibrous minerals such as kyanite. Uneven fracture is a surface or one with random irregularities. It occurs in a range of minerals including arsenopyrite, pyrite and magnetite. Rudolf Duda and Lubos Rejl, Minerals of the World http, //www. galleries. com/minerals/property/fracture. htm
13.
Mohs scale of mineral hardness
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The Mohs scale of mineral hardness is a qualitative ordinal scale characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. Created in 1812 by German geologist and mineralogist Friedrich Mohs, it is one of several definitions of hardness in materials science, while greatly facilitating the identification of minerals in the field, the Mohs scale does not show how well hard materials perform in an industrial setting. Despite its lack of precision, the Mohs scale is highly relevant for field geologists, the Mohs scale hardness of minerals can be commonly found in reference sheets. Reference materials may be expected to have a uniform Mohs hardness, the Mohs scale of mineral hardness is based on the ability of one natural sample of mineral to scratch another mineral visibly. The samples of matter used by Mohs are all different minerals, Minerals are pure substances found in nature. Rocks are made up of one or more minerals, as the hardest known naturally occurring substance when the scale was designed, diamonds are at the top of the scale. The hardness of a material is measured against the scale by finding the hardest material that the material can scratch. For example, if material is scratched by apatite but not by fluorite. Scratching a material for the purposes of the Mohs scale means creating non-elastic dislocations visible to the naked eye, frequently, materials that are lower on the Mohs scale can create microscopic, non-elastic dislocations on materials that have a higher Mohs number. The Mohs scale is an ordinal scale. For example, corundum is twice as hard as topaz, the table below shows the comparison with the absolute hardness measured by a sclerometer, with pictorial examples. On the Mohs scale, a streak plate has a hardness of 7.0, using these ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale. The table below incorporates additional substances that may fall between levels, Comparison between Hardness and Hardness, Mohs hardness of elements is taken from G. V, samsonov in Handbook of the physicochemical properties of the elements, IFI-Plenum, New York, USA,1968. The Hardness of Minerals and Rocks
14.
Lustre (mineralogy)
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Lustre or luster is the way light interacts with the surface of a crystal, rock, or mineral. The word traces its origins back to the latin lux, meaning light, a range of terms are used to describe lustre, such as earthy, metallic, greasy, and silky. Similarly, the term refers to a glassy lustre. A list of terms is given below. Lustre varies over a continuum, and so there are no rigid boundaries between the different types of lustre. The terms are frequently combined to describe types of lustre. Some minerals exhibit unusual optical phenomena, such as asterism or chatoyancy, a list of such phenomena is given below. Adamantine minerals possess a superlative lustre, which is most notably seen in diamond, such minerals are transparent or translucent, and have a high refractive index. Minerals with an adamantine lustre are uncommon, with examples being cerussite. Minerals with a degree of lustre are referred to as subadamantine, with some examples being garnet. Dull minerals exhibit little to no lustre, due to coarse granulations which scatter light in all directions, a distinction is sometimes drawn between dull minerals and earthy minerals, with the latter being coarser, and having even less lustre. Greasy minerals resemble fat or grease, a greasy lustre often occurs in minerals containing a great abundance of microscopic inclusions, with examples including opal and cordierite. Many minerals with a greasy lustre also feel greasy to the touch, metallic minerals have the lustre of polished metal, and with ideal surfaces will work as a reflective surface. Examples include galena, pyrite and magnetite, pearly minerals consist of thin transparent co-planar sheets. Light reflecting from these layers give them a lustre reminiscent of pearls, such minerals possess perfect cleavage, with examples including muscovite and stilbite. Resinous minerals have the appearance of resin, chewing gum or plastic, a principal example is amber, which is a form of fossilized resin. Silky minerals have an arrangement of extremely fine fibres, giving them a lustre reminiscent of silk. Examples include asbestos, ulexite and the satin spar variety of gypsum, a fibrous lustre is similar, but has a coarser texture
15.
Streak (mineralogy)
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The streak of a mineral is the color of the powder produced when it is dragged across an un-weathered surface. If no streak seems to be made, the streak is said to be white or colorless. Streak is particularly important as a diagnostic for opaque and colored materials and it is less useful for silicate minerals, most of which have a white streak or are too hard to powder easily. The apparent color of a mineral can vary widely because of impurities or a disturbed macroscopic crystal structure. Small amounts of an impurity that strongly absorbs a particular wavelength can radically change the wavelengths of light that are reflected by the specimen, and thus change the apparent color. However, when the specimen is dragged to produce a streak, it is broken into randomly oriented microscopic crystals, the surface across which the mineral is dragged is called a streak plate, and is generally made of unglazed porcelain tile. In the absence of a plate, the unglazed underside of a porcelain bowl or vase or the back of a glazed tile will work. Sometimes a streak is more easily or accurately described by comparing it with the streak made by another streak plate. Because the trail left behind results from the mineral being crushed into powder, in case of harder minerals, the color of the powder can be determined by filing or crushing with a hammer a small sample, which is then usually rubbed on a streak plate. Most minerals that are harder have a white streak. Some minerals leave a similar to their natural color, such as cinnabar. Other minerals leave surprising colors, such as fluorite, which always has a streak, although it can appear in purple, blue, yellow. Hematite, which is black in appearance, leaves a red streak which accounts for its name, galena, which can be similar in appearance to hematite, is easily distinguished by its gray streak. Hamilton, W. R. Cambridge Guide to Minerals, Rocks, the Encyclopedia of Gemstones and Minerals. New York, Facts on File. p.251, physical Characteristics of Minerals, at Introduction to Mineralogy by Andrea Bangert What is Streak
16.
Transparency and translucency
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In the field of optics, transparency is the physical property of allowing light to pass through the material without being scattered. On a macroscopic scale, the photons can be said to follow Snells Law, in other words, a translucent medium allows the transport of light while a transparent medium not only allows the transport of light but allows for image formation. The opposite property of translucency is opacity, transparent materials appear clear, with the overall appearance of one color, or any combination leading up to a brilliant spectrum of every color. When light encounters a material, it can interact with it in different ways. These interactions depend on the wavelength of the light and the nature of the material, photons interact with an object by some combination of reflection, absorption and transmission. Some materials, such as glass and clean water, transmit much of the light that falls on them and reflect little of it. Many liquids and aqueous solutions are highly transparent, absence of structural defects and molecular structure of most liquids are mostly responsible for excellent optical transmission. Materials which do not transmit light are called opaque, many such substances have a chemical composition which includes what are referred to as absorption centers. Many substances are selective in their absorption of light frequencies. They absorb certain portions of the spectrum while reflecting others. The frequencies of the spectrum which are not absorbed are either reflected or transmitted for our physical observation and this is what gives rise to color. The attenuation of light of all frequencies and wavelengths is due to the mechanisms of absorption. Transparency can provide almost perfect camouflage for animals able to achieve it and this is easier in dimly-lit or turbid seawater than in good illumination. Many marine animals such as jellyfish are highly transparent, at the atomic or molecular level, physical absorption in the infrared portion of the spectrum depends on the frequencies of atomic or molecular vibrations or chemical bonds, and on selection rules. Nitrogen and oxygen are not greenhouse gases because there is no absorption because there is no molecular dipole moment. With regard to the scattering of light, the most critical factor is the scale of any or all of these structural features relative to the wavelength of the light being scattered. Primary material considerations include, Crystalline structure, whether or not the atoms or molecules exhibit the long-range order evidenced in crystalline solids, glassy structure, scattering centers include fluctuations in density or composition. Microstructure, scattering centers include internal surfaces such as boundaries, crystallographic defects
17.
Specific gravity
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This page is about the measurement using water as a reference. For a general use of gravity, see relative density. See intensive property for the property implied by specific, Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is always water at its densest for liquids. Nonetheless, the temperature and pressure must be specified for both the sample and the reference, pressure is nearly always 1 atm. Temperatures for both sample and reference vary from industry to industry, in British beer brewing, the practice for specific gravity as specified above is to multiply it by 1000. Being a ratio of densities, specific gravity is a dimensionless quantity, Specific gravity varies with temperature and pressure, reference and sample must be compared at the same temperature and pressure or be corrected to a standard reference temperature and pressure. Substances with a gravity of 1 are neutrally buoyant in water. Those with SG greater than 1 are denser than water and will, disregarding surface tension effects and those with an SG less than 1 are less dense than water and will float on it. In scientific work, the relationship of mass to volume is expressed directly in terms of the density of the substance under study. It is in industry where specific gravity finds wide application, often for historical reasons. True specific gravity can be expressed mathematically as, S G true = ρ sample ρ H2 O where ρ sample is the density of the sample, the density of water varies with temperature and pressure as does the density of the sample. So it is necessary to specify the temperatures and pressures at which the densities or weights were determined and it is nearly always the case that measurements are made at 1 nominal atmosphere. For true specific gravity calculations, air pressure must be considered, temperatures are specified by the notation with T s representing the temperature at which the samples density was determined and T r the temperature at which the reference density is specified. For example, SG would be understood to mean that the density of the sample was determined at 20°C and of the water at 4°C. Taking into account different sample and reference temperatures, we note that, while S G H2 O =1.000000, it is also the case that S G H2 O =0.998203 /0.999840 =0.998363. Here, temperature is being specified using the current ITS-90 scale, on the previous IPTS-68 scale, the densities at 20 °C and 4 °C are 0.9982071 and 0.9999720 respectively, resulting in an SG value for water of 0.9982343. For example, in the industry, the Plato table lists sucrose concentration by weight against true SG
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Birefringence
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Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent, the birefringence is often quantified as the maximum difference between refractive indices exhibited by the material. Crystals with non-cubic crystal structures are often birefringent, as are plastics under mechanical stress and this effect was first described by the Danish scientist Rasmus Bartholin in 1669, who observed it in calcite, a crystal having one of the strongest birefringences. A mathematical description of wave propagation in a birefringent medium is presented below, following is a qualitative explanation of the phenomenon. Thus rotating the material around this axis does not change its optical behavior and this special direction is known as the optic axis of the material. Light whose polarization is perpendicular to the axis is governed by a refractive index no. Light whose polarization is in the direction of the optic axis sees an optical index ne, for any ray direction there is a linear polarization direction perpendicular to the optic axis, and this is called an ordinary ray. The magnitude of the difference is quantified by the birefringence, Δ n = n e − n o, the propagation of the ordinary ray is simply described by no as if there were no birefringence involved. However the extraordinary ray, as its name suggests, propagates unlike any wave in an optical material. Its refraction at a surface can be using the effective refractive index. However it is in fact an inhomogeneous wave whose power flow is not exactly in the direction of the wave vector and this causes an additional shift in that beam, even when launched at normal incidence, as is popularly observed using a crystal of calcite as photographed above. Rotating the calcite crystal will cause one of the two images, that of the ray, to rotate slightly around that of the ordinary ray. When the light propagates either along or orthogonal to the optic axis, in the first case, both polarizations see the same effective refractive index, so there is no extraordinary ray. In the second case the extraordinary ray propagates at a different phase velocity but is not an inhomogeneous wave, for instance, a quarter-wave plate is commonly used to create circular polarization from a linearly polarized source. The case of so-called biaxial crystals is substantially more complex and these are characterized by three refractive indices corresponding to three principal axes of the crystal. For most ray directions, both polarizations would be classified as extraordinary rays but with different effective refractive indices, being extraordinary waves, however, the direction of power flow is not identical to the direction of the wave vector in either case. The two refractive indices can be determined using the index ellipsoids for given directions of the polarization, note that for biaxial crystals the index ellipsoid will not be an ellipsoid of revolution but is described by three unequal principle refractive indices nα, nβ and nγ. Thus there is no axis around which a rotation leaves the optical properties invariant, for this reason, birefringent materials with three distinct refractive indices are called biaxial
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Titanium
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Titanium is a chemical element with symbol Ti and atomic number 22. It is a transition metal with a silver color, low density. Titanium is resistant to corrosion in sea water, aqua regia, titanium was discovered in Cornwall, Great Britain, by William Gregor in 1791, and it is named by Martin Heinrich Klaproth for the Titans of Greek mythology. The metal is extracted from its principal mineral ores by the Kroll, the most common compound, titanium dioxide, is a popular photocatalyst and is used in the manufacture of white pigments. Other compounds include titanium tetrachloride, a component of smoke screens and catalysts, and titanium trichloride, the two most useful properties of the metal are corrosion resistance and strength-to-density ratio, the highest of any metallic element. In its unalloyed condition, titanium is as strong as some steels, there are two allotropic forms and five naturally occurring isotopes of this element, 46Ti through 50Ti, with 48Ti being the most abundant. Although they have the number of valence electrons and are in the same group in the periodic table. As a metal, titanium is recognized for its high strength-to-weight ratio and it is a strong metal with low density that is quite ductile, lustrous, and metallic-white in color. The relatively high melting point makes it useful as a refractory metal and it is paramagnetic and has fairly low electrical and thermal conductivity. Commercial grades of titanium have ultimate tensile strength of about 434 MPa, equal to that of common, low-grade steel alloys, titanium is 60% denser than aluminium, but more than twice as strong as the most commonly used 6061-T6 aluminium alloy. Certain titanium alloys achieve tensile strengths of over 1400 MPa, however, titanium loses strength when heated above 430 °C. Titanium is not as hard as some grades of heat-treated steel, it is non-magnetic, machining requires precautions, because the material might gall unless sharp tools and proper cooling methods are used. Like steel structures, those made from titanium have a limit that guarantees longevity in some applications. The metal is an allotrope of an hexagonal α form that changes into a body-centered cubic β form at 882 °C. The specific heat of the α form increases dramatically as it is heated to this transition temperature but then falls, similar to zirconium and hafnium, an additional omega phase exists, which is thermodynamically stable at high pressures, but metastable at ambient pressures. This phase is usually hexagonal or trigonal and can be considered to be due to a soft longitudinal acoustic phonon of the β phase causing collapse of planes of atoms, like aluminium and magnesium, titanium metal and its alloys oxidize immediately upon exposure to air. Titanium readily reacts with oxygen at 1,200 °C in air and it is, however, slow to react with water and air at ambient temperatures because it forms a passive oxide coating that protects the bulk metal from further oxidation. When it first forms, this layer is only 1–2 nm thick but continues to grow slowly
20.
Titanium dioxide
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Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. When used as a pigment, it is called white, Pigment White 6. Generally it is sourced from ilmenite, rutile and anatase and it has a wide range of applications, from paint to sunscreen to food coloring. When used as a coloring, it has E number E171. World production in 2014 exceeded 9 million metric tons, one of these is known as akaogiite and should be considered as an extremely rare mineral. It is mainly sourced from ilmenite ore and this is the most widespread form of titanium dioxide-bearing ore around the world. Rutile is the next most abundant and contains around 98% titanium dioxide in the ore, the metastable anatase and brookite phases convert irreversibly to the equilibrium rutile phase upon heating above temperatures in the range 600–800 °C. Dubrovinsky and co-authors to be the hardest known oxide with the Vickers hardness of 38 GPa, however, later studies came to different conclusions with much lower values for both the hardness and bulk modulus. The oxides are commercially important ores of titanium, the metal can also be mined from other minerals such as ilmenite or leucoxene ores, or one of the purest forms, rutile beach sand. Star sapphires and rubies get their asterism from rutile impurities present in them, Titanium dioxide is found as a mineral in magmatic rocks and hydrothermal veins, as well as weathering rims on perovskite. TiO2 also forms lamellae in other minerals, spectral lines from titanium oxide are prominent in class M stars, which are cool enough to allow molecules of this chemical to form. The production method depends on the feedstock, the most common method for the production of titanium dioxide utilizes the mineral ilmenite. Ilmenite is mixed with sulfuric acid and this reacts to remove the iron oxide group in the ilmenite. The by-product iron sulfate is crystallized and filtered-off to yield only the salt in the digestion solution. This product is called synthetic rutile and this is further processed in a similar way to rutile to give the titanium dioxide product. Synthetic rutile and titanium slags are made especially for titanium dioxide production, the use of ilminite ore usually only produces pigment grade titanium dioxide. Another method for the production of synthetic rutile from ilmenite utilizes the Becher Process, rutile is the second most abundant mineral sand. Rutile found in primary rock cannot be extracted hence the deposits containing rutile sand can be mined meaning a reduced availability to the high concentration ore, crude titanium dioxide is purified via converting to titanium tetrachloride in the chloride process
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Corundum
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Corundum is a crystalline form of aluminium oxide typically containing traces of iron, titanium, vanadium and chromium. It is a transparent material, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red, all other colors are called sapphire, e. g. green sapphire for a green specimen. The name corundum is derived from the Tamil word Kurundam which originates from the Sanskrit word Kuruvinda meaning ruby, because of corundums hardness, it can scratch almost every other mineral. It is commonly used as an abrasive on everything from sandpaper to large machines used in machining metals, plastics, some emery is a mix of corundum and other substances, and the mix is less abrasive, with an average Mohs hardness of 8.0. In addition to its hardness, corundum is unusual for its density of 4.02 g/cm3, corundum occurs as a mineral in mica schist, gneiss, and some marbles in metamorphic terranes. It also occurs in low silica igneous syenite and nepheline syenite intrusives, other occurrences are as masses adjacent to ultramafic intrusives, associated with lamprophyre dikes and as large crystals in pegmatites. It commonly occurs as a mineral in stream and beach sands because of its hardness. The largest documented crystal of corundum measured about 65×40×40 cm. The record has since surpassed by certain synthetic boules. Corundum for abrasives is mined in Zimbabwe, Russia, Sri Lanka, historically it was mined from deposits associated with dunites in North Carolina, US and from a nepheline syenite in Craigmont, Ontario. Emery-grade corundum is found on the Greek island of Naxos and near Peekskill, New York, abrasive corundum is synthetically manufactured from bauxite. Four corundum axes dating back to 2500 BCE from the Liangzhou culture have been discovered in China, in 1837, Marc Antoine Gaudin made the first synthetic rubies by fusing alumina at a high temperature with a small amount of chromium as a pigment. In 1847, Ebelmen made white synthetic sapphires by fusing alumina in boric acid, in 1877 Frenic and Freil made crystal corundum from which small stones could be cut. Frimy and Auguste Verneuil manufactured artificial ruby by fusing BaF2, in 1903, Verneuil announced he could produce synthetic rubies on a commercial scale using this flame fusion process. The Verneuil process allows the production of flawless single-crystal sapphires, rubies and it is also possible to grow gem-quality synthetic corundum by flux-growth and hydrothermal synthesis. Corundum crystallizes with trigonal symmetry in the space group R3c and has the lattice parameters a =4.75 Å and c =12.982 Å at standard conditions, the unit cell contains six formula units. In the lattice of corundum, the atoms form a slightly distorted hexagonal close packing
22.
Spin states (d electrons)
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Spin states when describing transition metal coordination complexes refers to the potential spin configurations of the metal centers d electrons. In many these spin states vary between high-spin and low-spin configurations, the Δ splitting of the d orbitals plays an important role in the electron spin state of a coordination complex. There are three factors that affect the Δ, the period of the ion, the charge of the metal ion. If the energy required to two electrons is greater than the energy cost of placing an electron in an eg, Δ. If the separation between the orbitals is large, then the lower energy orbitals are filled before population of the higher orbitals according to the Aufbau principle. Complexes such as this are called low-spin since filling an orbital matches electrons, so, one electron is put into each of the five d orbitals before any pairing occurs in accord with Hunds rule resulting in what is known as a high-spin complex. Complexes such as this are called high-spin since populating the upper orbital avoids matches between electrons with opposite spin, within a transition metal group moving down the series corresponds with an increase in Δ. The observed result is larger Δ splitting for complexes in octahedral geometries based around transition metal centers of the second or third row and this Δ splitting is generally large enough that these complexes do not exist as high-spin state. This is true even when the center is coordinated to weak field ligands. It is only octahedral coordination complexes which are centered on first row transition metals that fluctuate between high and low-spin states, the charge of the metal center plays a role in the ligand field and the Δ splitting. For example, Fe2+ and Co3+ are both d6, however, the charge of Co3+ creates a stronger ligand field than Fe2+. All other things being equal, Fe2+ is more likely to be high spin than Co3+, ligands also affect the magnitude of Δ splitting of the d orbitals according to their field strength as described by the spectrochemical series. Strong-field ligands, such as CN− and CO, increase the Δ splitting and are likely to be low-spin. Weak-field ligands, such as I− and Br− cause a smaller Δ splitting and are likely to be high-spin. The Δ splitting energy for tetrahedral metal complexes, Δtet is smaller than that for an octahedral complex and it is unknown to have a Δtet sufficient to overcome the spin pairing energy. Tetrahedral complexes are always high spin, there are no known ligands powerful enough to produce the strong-field case in a tetrahedral complex Most spin-state transitions are between the same geometry, namely octahedral. However, in the case of d8 complexes is a shift in geometry between spin states, there is no possible difference between the high and low-spin states in the d8 octahedral complexes. However, d8 complexes are able to shift from paramagnetic tetrahedral geometry to a diamagnetic low-spin square planar geometry, the rationale for why the spin states exist according to ligand field theory is essentially the same as the crystal field theory explanation
23.
Mineral
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A mineral is a naturally occurring chemical compound, usually of crystalline form and abiogenic in origin. A mineral has one specific chemical composition, whereas a rock can be an aggregate of different minerals or mineraloids, the study of minerals is called mineralogy. There are over 5,300 known mineral species, over 5,070 of these have been approved by the International Mineralogical Association, the silicate minerals compose over 90% of the Earths crust. The diversity and abundance of species is controlled by the Earths chemistry. Silicon and oxygen constitute approximately 75% of the Earths crust, which translates directly into the predominance of silicate minerals, minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various species, changes in the temperature, pressure, or bulk composition of a rock mass cause changes in its minerals. Minerals can be described by their various properties, which are related to their chemical structure. Common distinguishing characteristics include crystal structure and habit, hardness, lustre, diaphaneity, colour, streak, tenacity, cleavage, fracture, parting, more specific tests for describing minerals include magnetism, taste or smell, radioactivity and reaction to acid. Minerals are classified by key chemical constituents, the two dominant systems are the Dana classification and the Strunz classification, the silicate class of minerals is subdivided into six subclasses by the degree of polymerization in the chemical structure. All silicate minerals have a unit of a 4− silica tetrahedron—that is, a silicon cation coordinated by four oxygen anions. These tetrahedra can be polymerized to give the subclasses, orthosilicates, disilicates, cyclosilicates, inosilicates, phyllosilicates, other important mineral groups include the native elements, sulfides, oxides, halides, carbonates, sulfates, and phosphates. The first criterion means that a mineral has to form by a natural process, stability at room temperature, in the simplest sense, is synonymous to the mineral being solid. More specifically, a compound has to be stable or metastable at 25 °C, modern advances have included extensive study of liquid crystals, which also extensively involve mineralogy. Minerals are chemical compounds, and as such they can be described by fixed or a variable formula, many mineral groups and species are composed of a solid solution, pure substances are not usually found because of contamination or chemical substitution. Finally, the requirement of an ordered atomic arrangement is usually synonymous with crystallinity, however, crystals are also periodic, an ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form, hardness, and cleavage. There have been recent proposals to amend the definition to consider biogenic or amorphous substances as minerals. The formal definition of an approved by the IMA in 1995, A mineral is an element or chemical compound that is normally crystalline. However, if geological processes were involved in the genesis of the compound, Mineral classification schemes and their definitions are evolving to match recent advances in mineral science
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Magnetite
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Magnetite is a mineral and one of the main iron ores. With the chemical formula Fe3O4, it is one of the oxides of iron, Magnetite is ferrimagnetic, it is attracted to a magnet and can be magnetized to become a permanent magnet itself. It is the most magnetic of all the minerals on Earth. Naturally-magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, today it is mined as iron ore. Small grains of magnetite occur in almost all igneous and metamorphic rocks, Magnetite is black or brownish-black with a metallic luster, has a Mohs hardness of 5–6 and leaves a black streak. The chemical IUPAC name is iron oxide and the chemical name is ferrous-ferric oxide. In addition to rocks, magnetite also occurs in sedimentary rocks, including banded iron formations and in lake. Magnetite nanoparticles are also thought to form in soils, where they probably oxidize rapidly to maghemite, Magnetite has an inverse spinel crystal structure. As a member of the group, it can form solid solutions with similarly structured minerals, including ulvospinel. Titanomagnetite, also known as titaniferous magnetite, is a solution between magnetite and ulvospinel that crystallizes in many mafic igneous rocks. Titanomagnetite may undergo oxyexsolution during cooling, resulting in ingrowths of magnetite and ilmenite, Magnetite has been important in understanding the conditions under which rocks form. Magnetite reacts with oxygen to produce hematite, and the pair forms a buffer that can control oxygen fugacity. Commonly, igneous rocks contain solid solutions of both titanomagnetite and hemoilmenite or titanohematite, Magnetite also is produced from peridotites and dunites by serpentinization. Lodestones were used as a form of magnetic compass. At low temperatures, magnetite undergoes a crystal structure phase transition from a structure to a cubic structure known as the Verwey transition. The Verwey transition occurs around 121 K and is dependent on size, domain state. An isotropic point also occurs near the Verwey transition around 130 K, the Curie temperature of magnetite is 858 K. Magnetite is sometimes found in large quantities in beach sand. Such black sands are found in places, such as Lung Kwu Tan of Hong Kong, California of the United States
25.
Pleochroism
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Pleochroism is an optical phenomenon in which a substance appears to be different colors when observed at different angles, especially with polarized light. Anisotropic crystals will have properties that vary with the direction of light. The polarization of light determines the direction of the electric field and these kinds of crystals have one or two optical axes. If absorption of light varies with the relative to the optical axis in a crystal then pleochroism results. Anisotropic crystals have double refraction of light where light of different polarizations is bent different amounts by the crystal, the components of a divided light beam follow different paths within the mineral and travel at different speeds. When the mineral is observed at some angle, light following some combination of paths and polarizations will be present, at another angle, the light passing through the crystal will be composed of another combination of light paths and polarizations, each with their own color. The light passing through the mineral will therefore have different colors when it is viewed from different angles, tetragonal, trigonal and hexagonal minerals can only show two colors and are called dichroic. Orthorhombic, monoclinic and triclinic crystals can show three and are trichroic, for example, hypersthene, with two optical axes, can have red, yellow or blue appearance when oriented in three different ways in three-dimensional space. Tourmaline is notable for exhibiting strong pleochroism, gems are sometimes cut and set either to display pleochroism or to hide it, depending on the colors and their attractiveness. The pleochroic colours are at their maximum when light is polarized parallel with a crystallographic axis, the axes are designated X, Y and Z. These axes can be determined from the appearance of a crystal in an interference pattern. Where there are two axes, the acute bisection of the axes gives Z for positive minerals and X for negative minerals. Perpendicular to these is the Y axis, the colour is measured with the polarization parallel to each direction. An absorption formula records the amount of parallel to each axis in the form of X < Y < Z with the left most having the least absorption. Minerals that are very similar often have very different pleochroic color schemes. In such cases, a section of the mineral is used and examined under polarized transmitted light with a petrographic microscope. Another device using this property to identify minerals is the dichroscope
26.
Manaccan
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Manaccan is a civil parish and village on the Lizard peninsula in south Cornwall, England, United Kingdom. The village is five miles south-southwest of Falmouth. Manaccan parish is in a known as Meneage which means land of the monks. The parish is bordered to the north by the Helford River, to the west by St Martin-in-Meneage parish, to the south by St Keverne parish, the origin of the name Manaccan is probably derived not from a saint but from the Cornish for of the monks. It was also at times called Minster in English because it must once have had a Celtic monastery, St Manacca is recorded as the patron as early as 1308. The population of Manaccan was 321 in the 2011 census, an increase from 299 in the 2001 census, Manaccan lies within the Cornwall Area of Outstanding Natural Beauty. Almost a third of Cornwall has AONB designation, with the same status, the parish church is dedicated to St Mannacus and St Dunstan. There was a Norman church here and fragments of it remain, the rest of the structure is of the 13th and 15th centuries. The west tower is built of slate, the church is well known for a large and flourishing fig-tree which is growing out of the western part of the south wall of the church. It has been there for at least 250 years, boden Vean Fogou was rediscovered by a local farmer in the 1990s and was excavated by archaeologists in 2003 and in September and October 2008. In 1791 William Gregor discovered titanium in the stream runs through the valley just south of the village. The location is commemorated by a plaque placed next to the bridge, the mineral ilmenite, an iron titanium oxide, was a constituent of the ore identified by William Gregor, it has an alternative name manaccanite, derived from Manaccan. Thomas Flindell, newspaper publisher, was born at Helford in the parish, brigadier-General Francis Stewart Montague-Bates was born and died at Manaccan Richard Polwhele, clergyman and historian, Vicar of Manaccan. Polwhele was non-resident at Manaccan from 1806, he angered Manaccan parishioners with his efforts to restore the church, genealogy & History Resources for Manaccan
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Cornwall
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Cornwall is a ceremonial county and unitary authority area of England within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, Cornwall has a population of 551,700 and covers an area of 3,563 km2. Cornwall forms the westernmost part of the south-west peninsula of the island of Great Britain, and this area was first inhabited in the Palaeolithic and Mesolithic periods. It continued to be occupied by Neolithic and then Bronze Age peoples, there is little evidence that Roman rule was effective west of Exeter and few Roman remains have been found. In the mid-19th century, however, the tin and copper mines entered a period of decline, subsequently, china clay extraction became more important and metal mining had virtually ended by the 1990s. Traditionally, fishing and agriculture were the important sectors of the economy. Railways led to a growth of tourism in the 20th century, however, the area is noted for its wild moorland landscapes, its long and varied coastline, its attractive villages, its many place-names derived from the Cornish language, and its very mild climate. Extensive stretches of Cornwalls coastline, and Bodmin Moor, are protected as an Area of Outstanding Natural Beauty, Cornwall is the homeland of the Cornish people and is recognised as one of the Celtic nations, retaining a distinct cultural identity that reflects its history. Some people question the present constitutional status of Cornwall, and a nationalist movement seeks greater autonomy within the United Kingdom in the form of a devolved legislative Cornish Assembly. On 24 April 2014 it was announced that Cornish people will be granted minority status under the European Framework Convention for the Protection of National Minorities. The modern English name Cornwall derives from the concatenation of two ancient demonyms from different linguistic traditions, Corn- records the native Brythonic tribe, the Cornovii. The Celtic word kernou is cognate with the English word horn. -wall derives from the Old English exonym walh, the Ravenna Cosmography first mentions a city named Purocoronavis in the locality. This is thought to be a rendering of Duro-cornov-ium, meaning fort of the Cornovii. The exact location of Durocornovium is disputed, with Tintagel and Carn Brea suggested as possible sites, in later times, Cornwall was known to the Anglo-Saxons as West Wales to distinguish it from North Wales. The name appears in the Anglo-Saxon Chronicle in 891 as On Corn walum, in the Domesday Book it was referred to as Cornualia and in c.1198 as Cornwal. Other names for the county include a latinisation of the name as Cornubia, the present human history of Cornwall begins with the reoccupation of Britain after the last Ice Age. The area now known as Cornwall was first inhabited in the Palaeolithic and Mesolithic periods and it continued to be occupied by Neolithic and then Bronze Age people. The Common Brittonic spoken at the time developed into several distinct tongues
28.
Geikielite
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Geikielite is a magnesium titanium oxide mineral with formula, MgTiO3. It is a member of the ilmenite group and it crystallizes in the trigonal system forming typically opaque, black to reddish black crystals. It was first described in 1892 for an occurrence in the Ceylonese gem bearing gravel placers and it was named for Scottish geologist Sir Archibald Geikie. It occurs in metamorphosed impure magnesian limestones, in serpentinite derived from ultramafic rocks, associated minerals include rutile, spinel, clinohumite, perovskite, diopside, serpentine, forsterite, brucite, hydrotalcite, chlorite and calcite. Ghiorso, Mark S. Thermodynamic properties of hematite — Ilmenite — Geikielite solid solutions, guyot, F. High-temperature properties of geikielite from high-temperature high-pressure Raman spectroscopy. Baura-Peña, M. P. Martínez-Lope, M. J. García-Clavel, heat capacities and entropies at 298.15 K of MgTiO3, ZnO, and ZnCO3. Titanian clinohumite and geikielite in marbles from the Bergell contact aureole, electrical resistivity of nano-crystalline and natural MgTiO3−geikielite at high-pressures up to 8 GPa. Mitchell, Jeremy N. Yu, Ning, Sickafus, Kurt E. Nastasi, Michael A. McClellan, Kenneth J. Ion irradiation damage in geikielite
29.
Solid solution
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A solid solution is a solid-state solution of one or more solutes in a solvent. The solid solution needs to be distinguished from a mechanical mixtures of powdered solids like two salts, sugar and salt, etc, the mechanical mixtures have total or partial miscibility gap in solid state. Examples of solid solutions include crystallized salts from their liquid mixture, metal alloys, in the case of metal alloys intermetallic compounds occur frequently. The solute may incorporate into the solvent crystal lattice substitutionally, by replacing a solvent particle in the lattice, or interstitially, by fitting into the space between solvent particles. Both of these types of solid solution affect the properties of the material by distorting the crystal lattice, some mixtures will readily form solid solutions over a range of concentrations, while other mixtures will not form solid solutions at all. The propensity for any two substances to form a solution is a complicated matter involving the chemical, crystallographic. 1 displays an alloy of two metals which forms a solution at all relative concentrations of the two species. Solid solutions have important commercial and industrial applications, as such mixtures often have superior properties to pure materials, many metal alloys are solid solutions. Even small amounts of solute can affect the electrical and physical properties of the solvent, the binary phase diagram in Fig.2 shows the phases of a mixture of two substances in varying concentrations, A and B. The region labeled α is a solution, with B acting as the solute in a matrix of A. On the other end of the scale, the region labeled β is also a solid solution. The large solid region in between the α and β solid solutions, labeled α + β, is not a solid solution, at other proportions, the material will enter a mushy or pasty phase until it warms up to being completely melted. The mixture at the dip point of the diagram is called a eutectic alloy, lead-tin mixtures formulated at that point are useful when soldering electronic components, particularly if done manually, since the solid phase is quickly entered as the solder cools. In contrast, when lead-tin mixtures were used to solder seams in automobile bodies a pasty state enabled a shape to be formed with a paddle or tool. When a solid solution becomes unstable — due to a temperature, for example — exsolution occurs. This is mainly caused by difference in cation size, cations which have a large difference in radii are not likely to readily substitute. Take the alkali feldspar minerals for example, whose end members are albite, NaAlSi3O8 and microcline and this leads to exsolution where they will separate into two separate phases. In the case of the feldspar minerals, thin white albite layers will alternate between typically pink microcline
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Kimberlite
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Kimberlite is an igneous rock best known for sometimes containing diamonds. Kimberlite occurs in the Earths crust in vertical structures known as kimberlite pipes as well as igneous dykes, Kimberlite also occurs as horizontal sills. Kimberlite pipes are the most important source of mined diamonds today, the consensus on kimberlites is that they are formed deep within the mantle. It is this depth of melting and generation which makes kimberlites prone to hosting diamond xenocrysts, despite its relative rarity, kimberlite has attracted attention because it serves as a carrier of diamonds and garnet peridotite mantle xenoliths to the Earths surface. Many kimberlite structures are emplaced as carrot-shaped, vertical intrusions termed pipes, Kimberlite classification is based on the recognition of differing rock facies. These differing facies are associated with a style of magmatic activity, namely crater, diatreme. The morphology of kimberlite pipes, and their classical carrot shape is the result of explosive volcanism from very deep mantle-derived sources. These volcanic explosions produce vertical columns of rock rise from deep magma reservoirs. The morphology of kimberlite pipes is varied but includes a sheeted dyke complex of tabular, within 1. 5–2 km of the surface, the highly pressured magma explodes upwards and expands to form a conical to cylindrical diatreme, which erupts to the surface. The surface expression is rarely preserved but is similar to a maar volcano. The diameter of a pipe at the surface is typically a few hundred meters to a kilometer. Two Jurassic kimberlite dikes exist in Pennsylvania, one, the Gates-Adah Dike, outcrops on the Monongahela River on the border of Fayette and Greene Counties. The other, the Dixonville-Tanoma Dike in central Indiana County, does not outcrop at the surface and was discovered by miners, similarly aged kimberlite is found in several locations in New York Both the location and origin of kimberlitic magmas are subjects of contention. The mechanism of enrichment has also been the topic of interest with models including partial melting, historically, kimberlites have been classified into two distinct varieties termed basaltic and micaceous based primarily on petrographic observations. This was later revised by Smith who renamed these divisions Group I and Group II based on the affinities of these rocks using the Nd, Sr. Mitchell later proposed that these group I and II kimberlites display such distinct differences and he showed that Group II kimberlites show closer affinities to lamproites than they do to Group I kimberlites. Hence, he reclassified Group II kimberlites as orangeites to prevent confusion, olivine lamproites were previously called Group II kimberlite or orangeite in response to the mistaken belief that they only occurred in South Africa. Their occurrence and petrology, however, are identical globally and should not be referred to as kimberlite
31.
Felsic
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In geology, felsic refers to igneous rocks that are relatively rich in elements that form feldspar and quartz. It is contrasted with mafic rocks, which are richer in magnesium. It refers to those rocks rich in minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium. They are usually light in color and have specific gravities less than 3, the most common felsic rock is granite. Common felsic minerals include quartz, muscovite, orthoclase, and the sodium-rich plagioclase feldspars, in terms of chemistry, felsic minerals and rocks are at the other end of the elemental spectrum from the mafic minerals and rocks. In modern usage, the acid rock, although sometimes used as a synonym, refers to a high-silica-content volcanic rock. The term was used broadly in older geologic literature. It is considered archaic now, as the acidic and basic rock were based on an incorrect idea, dating from the 19th century. The term felsic combines the words feldspar and silica, in order for a rock to be classified as felsic, it generally needs to contain more than 75% felsic minerals, namely quartz, orthoclase and plagioclase. Rocks with greater than 90% felsic minerals can also be called leucocratic, the chemical name of a felsic rock is given according to the TAS classification of Le Maitre. However, this applies to volcanic rocks. If the rock is analyzed and found to be felsic but is metamorphic and has no definite volcanic protolith, there are examples known of highly sheared granites which can be mistaken for rhyolites. For phaneritic felsic rocks, the QAPF diagram should be used, the rock texture thus determines the basic name of a felsic rock. QAPF diagram List of minerals List of rock types Le Maitre, igneous Rocks, A Classification and Glossary of Terms 2nd edition, Cambridge
32.
Hematite
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Hematite, also spelled as haematite, is the mineral form of iron oxide, one of several iron oxides. Hematite crystallizes in the lattice system, and it has the same crystal structure as ilmenite. Hematite and ilmenite form a solid solution at temperatures above 950 °C. Hematite is colored black to steel or silver-gray, brown to reddish brown and it is mined as the main ore of iron. Varieties include kidney ore, martite, iron rose and specularite, while the forms of hematite vary, they all have a rust-red streak. Hematite is harder than iron, but much more brittle. Maghemite is a hematite- and magnetite-related oxide mineral, huge deposits of hematite are found in banded iron formations. Gray hematite is typically found in places that can have still standing water or mineral hot springs, the mineral can precipitate out of water and collect in layers at the bottom of a lake, spring, or other standing water. Hematite can also occur without water, however, usually as the result of volcanic activity, the name hematite is derived from the Greek word for blood αἷμα haima, due to the red coloration found in some varities of hematite. The color of hematite lends itself to use as a pigment, ochre is a clay that is colored by varying amounts of hematite, varying between 20% and 70%. Red ochre contains unhydrated hematite, whereas yellow ochre contains hydrated hematite, the principal use of ochre is for tinting with a permanent color. The red chalk writing of this mineral was one of the earliest in the history of humans, the powdery mineral was first used 164,000 years ago by the Pinnacle-Point man possibly for social purposes. Hematite residues are found in graves from 80,000 years ago. Near Rydno in Poland and Lovas in Hungary red chalk mines have been found that are from 5000 BC, rich deposits of hematite have been found on the island of Elba that have been mined since the time of the Etruscans. Adding to the surprise was a transition with a decrease in temperature at around 260 K to a phase with no net magnetic moment. The disappearance of the moment with a decrease in temperature at 260 K is caused by a change in the anisotropy which causes the moments to align along the c axis, in this configuration, spin canting does not reduce the energy. The magnetic properties of bulk hematite differ from their nanoscale counterparts, for example, the Morin transition temperature of hematite decreases with a decrease in the particle size. Two other end-members are referred to as protohematite and hydrohematite, enhanced magnetic coercivities for hematite have been achieved by dry-heating a 2-line ferrihydrite precursor prepared from solution
33.
Metasomatism
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Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids. It is the replacement of one rock by another of different minerological and chemical composition, the minerals which compose the rocks are dissolved and new mineral formations are deposited in their place. Dissolution and deposition occur simultaneously and the rock remains solid, synonyms to the word metasomatism are metasomatose and metasomatic process. The word metasomatose can also be used as a name for specific varieties of metasomatism, metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source. In the igneous environment, metasomatism creates skarns, greisen, because metamorphism usually requires water in order to facilitate metamorphic reactions, metasomatism and metamorphism nearly always occur together. Further, because metasomatism is a transfer process, it is not restricted to the rocks which are changed by addition of chemical elements. In all cases, to produce a rock some other rock is also metasomatised. The source region is often largely chemically unaffected compared to the highly hydrated, altered shear zones, metasomatism is thought to be particularly important in changing the composition of mantle peridotite below island arcs as water is driven out of ocean lithosphere during subduction. Metasomatism has also been considered critical for enriching source regions of some silica-undersaturated magmas, carbonatite melts are often considered to have been responsible for enrichment of mantle peridotite in incompatible elements. Metasomatic rocks can be extremely varied, often, metasomatised rocks are pervasively but weakly altered, such that the only evidence of alteration is bleaching, change in colour or change in the crystallinity of micaceous minerals. In some cases, geochemical evidence can be found of metasomatic alteration processes and this is usually in the form of mobile, soluble elements such as barium, strontium, rubidium, calcium and some rare earth elements. However, to characterise the alteration properly, it is necessary to compare altered with unaltered samples, Skarn and skarnoid rock types, typically adjacent to granite intrusions and adjacent to reactive lithologies such as limestone, marl and banded iron formation. Greisen deposits within granite margins and cupolas, effects of metasomatism in mantle peridotite can be either modal or cryptic. In cryptic metasomatism, mineral compositions are changed, or introduced elements are concentrated on grain boundaries, in modal metasomatism, new minerals are formed. Cryptic metasomatism may be caused as rising or percolating melts interact with surrounding peridotite, formation of minerals less common in peridotite, such as dolomite, calcite, ilmenite, rutile, and armalcolite, is also attributed to melt or fluid metasomatism. Stressed minerals and country rocks of granitic plutons are replaced by porphyroblasts of orthoclase and quartz, Mantle volatiles -- distribution and consequences. In The Mantle and Core Volume 2 Treatise on Geochemistry, Elsevier-Pergamon, Oxford, ISBN 0-08-043751-6 Hydrothermal Ore genesis Greisen Skarn Hornfels Pneumatolysis
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Gabbro
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Gabbro refers to a large group of dark, often phaneritic, mafic intrusive igneous rocks chemically equivalent to basalt. It forms when magma is trapped beneath the Earths surface. Much of the Earths oceanic crust is made of gabbro, formed at mid-ocean ridges, Gabbro is also found as plutons associated with continental volcanism. Due to its variant nature, the term gabbro may be applied loosely to a range of intrusive rocks. The term gabbro was used in the 1760s to name a set of types that were found in the ophiolites of the Apennine Mountains in Italy. Then, in 1809, the German geologist Christian Leopold von Buch used the term more restrictively in his description of these Italian ophiolitic rocks and he assigned the name gabbro to rocks that geologists nowadays would more strictly call metagabbro. Von Buch named gabbro after Gabbro, a village in Rosignano Marittimo municipality of Tuscany, Gabbro is dense, greenish or dark-colored and contains pyroxene, plagioclase, and minor amounts of amphibole and olivine. The pyroxene content is mostly clinopyroxene, generally augite, but small amounts of orthopyroxene may also be present, if the amount of orthopyroxene is more than 95% of the total pyroxene content, then the rock is termed norite. On the other hand, gabbro has more than 95% of its pyroxenes in the form of the monoclinic clinopyroxene/s, the calcium rich plagioclase feldspar and pyroxene content vary between 10% - 90% in gabbro. If more than 90% plagioclase is present, then the rock is an anorthosite, if on the other hand, the rock contains more than 90% pyroxenes, it is termed pyroxenite. Gabbro may also contain amounts of olivine, amphibole and biotite. The quartz content in gabbro is less than 5% of total volume, quartz gabbros or monzogabbros are also known to occur, for example the cizlakite at Pohorje in northeastern Slovenia, and are probably derived from magma that was over-saturated with silica. Gabbros contain minor amounts, typically a few percent, of iron-titanium oxides such as magnetite, ilmenite, Gabbro is generally coarse grained, with crystals in the size range of 1 mm or greater. Finer grained equivalents of gabbro are called diabase, although the term microgabbro is often used when extra descriptiveness is desired, Gabbro may be extremely coarse grained to pegmatitic, and some pyroxene-plagioclase cumulates are essentially coarse grained gabbro, some may exhibit acicular crystal habits. Gabbro is usually equigranular in texture, although it may be porphyritic at times, cumulate gabbros are more properly termed pyroxene-plagioclase adcumulate. Gabbro is an part of the oceanic crust, and can be found in many ophiolite complexes as parts of zones III. Long belts of gabbroic intrusions are typically formed at proto-rift zones and around ancient rift zone margins, mantle plume hypotheses may rely on identifying mafic and ultramafic intrusions and coeval basalt volcanism. It is better to base a rock definition on descriptive characteristics of the rather than how or where it was formed
35.
Diorite
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Diorite is an intrusive igneous rock composed principally of the silicate minerals plagioclase feldspar, biotite, hornblende, and/or pyroxene. The chemical composition of diorite is intermediate, between that of gabbro and felsic granite. Diorite is usually grey to dark-grey in colour, but it can also be black or bluish-grey and it is distinguished from gabbro on the basis of the composition of the plagioclase species, the plagioclase in diorite is richer in sodium and poorer in calcium. Diorite may contain small amounts of quartz, microcline, and olivine, zircon, apatite, titanite, magnetite, ilmenite, and sulfides occur as accessory minerals. Minor amounts of muscovite may also be present, varieties deficient in hornblende and other dark minerals are called leucodiorite. When olivine and more iron-rich augite are present, the grades into ferrodiorite. The presence of significant quartz makes the rock type quartz-diorite or tonalite, and if orthoclase is present at greater than 10 percent, a dioritic rock containing feldspathoid mineral/s and no quartz is termed foid-bearing diorite or foid diorite according to content. Diorite has a phaneritic, often speckled, texture of coarse grain size and is occasionally porphyritic, orbicular diorite shows alternating concentric growth bands of plagioclase and amphibole surrounding a nucleus, within a diorite porphyry matrix. Diorites may be associated with granite or gabbro intrusions, into which they may subtly merge. Diorite results from the melting of a mafic rock above a subduction zone. It is commonly produced in volcanic arcs, and in mountain building, such as in the Andes Mountains. The extrusive volcanic equivalent rock type is andesite, diorite is an extremely hard rock, making it difficult to carve grand work with. It is so hard that ancient civilizations used diorite balls to work granite and its hardness, however, also allows it to be worked finely and take a high polish, and to provide a durable finished work. One comparatively frequent use of diorite was for inscription, as it is easier to carve in relief than in three-dimensional statuary, perhaps the most famous diorite work extant is the Code of Hammurabi, inscribed upon a 2.23 m pillar of black diorite. The original can be today in Paris Musée du Louvre. The use of diorite in art was most important among very early Middle Eastern civilizations such as Ancient Egypt, Babylonia, Assyria, and Sumer. It was so valued in early times that the first great Mesopotamian empire—the Empire of Sargon of Akkad—listed the taking of diorite as a purpose of military expeditions. Although one can find diorite art from later periods, it more popular as a structural stone and was frequently used as pavement due to its durability
36.
Sokndal
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Sokndal is the southernmost municipality in Rogaland county, Norway. It is located in the district of Dalane. The administrative centre of the municipality is the village of Hauge, other villages in Sokndal include Li, Rekefjord, Sogndalsstranda, and Åna-Sira. Sogndalsstranda is a picturesque, old fishing village, which may have inspired the municipality in becoming Norways first member of Cittaslow, the Jøssingfjorden, known for the Altmark Incident, is also located in Sokndal. The parish of Soggendal was established as a municipality on 1 January 1838, in 1845, the small lading place of Sogndal was separated from Sokndal as a municipality of its own. This left Sokndal with 2,819 residents, on 12 December 1868, a small part of Sokndal was transferred to neighboring Eigersund municipality. On 1 July 1944, the small lading place of Sogndal was reincorporated into Sokndal, in 1947, a small area in Sokndal was transferred to Eigersund. On 1 January 1967, the Tjørn farm was transferred from Eigersund to Sokndal, the Old Norse form of the name was Sóknardalr. The first element is the case of the river name Sókn. The river name is derived from the Old Norse verb sœkja which means seek, before 1918, the name was written Sogndal or Soggendahl. The coat-of-arms is from modern times, they were granted on 8 July 1988, the arms show three black pickaxes on a yellow background. These were chosen to symbolize the importance of mining and agriculture in the municipality and it was designed by Johan Digernes of Haugesund. The Church of Norway has one parish within the municipality of Sokndal and it is part of the Dalane deanery in the Diocese of Stavanger. The municipality is the southernmost in Rogaland county, the lakes Grøsfjellvatnet and Eiavatnet both lie on the northern border of the municipality. The coastline of Sokndal is fairly smooth, although there are two larger fjords which cut into the municipality, the Rekefjorden and Jøssingfjorden, the Lille Presteskjær Lighthouse marks the entrance to the Rekefjorden. The southeastern part of the municipality is very rocky and rugged and it is the site of the large Tellnes mine, a large producer of titanium. At Tellnes, just east of Hauge i Dalane, there is a mine run by Titania AS. Its also the worlds largest opencast ilmenite mine, the municipality is governed by a municipal council of elected representatives, which in turn elect a mayor
37.
Metamorphic rock
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Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means change in form. The original rock is subjected to heat and pressure, causing profound physical and/or chemical change, the protolith may be a sedimentary, an igneous, or even an existing type of metamorphic rock. Metamorphic rocks make up a part of the Earths crust. They are classified by texture and by chemical and mineral assemblage and they may be formed simply by being deep beneath the Earths surface, subjected to high temperatures and the great pressure of the rock layers above it. They can form from tectonic processes such as continental collisions, which cause horizontal pressure and they are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earths interior. The study of rocks provides information about the temperatures and pressures that occur at great depths within the Earths crust. Some examples of rocks are gneiss, slate, marble, schist. Metamorphic minerals are those that only at the high temperatures and pressures associated with the process of metamorphism. These minerals, known as index minerals, include sillimanite, kyanite, staurolite, andalusite, and some garnet. Other minerals, such as olivines, pyroxenes, amphiboles, micas, feldspars, and quartz, may be found in metamorphic rocks and these minerals formed during the crystallization of igneous rocks. They are stable at temperatures and pressures and may remain chemically unchanged during the metamorphic process. However, all minerals are only within certain limits. The change in the size of the rock during the process of metamorphism is called recrystallization. Both high temperatures and pressures contribute to recrystallization, high temperatures allow the atoms and ions in solid crystals to migrate, thus reorganizing the crystals, while high pressures cause solution of the crystals within the rock at their point of contact. The layering within metamorphic rocks is called foliation, and it occurs when a rock is being shortened along one axis during recrystallization. This causes the platy or elongated crystals of minerals, such as mica and chlorite and this results in a banded, or foliated rock, with the bands showing the colors of the minerals that formed them. Textures are separated into foliated and non-foliated categories, foliated rock is a product of differential stress that deforms the rock in one plane, sometimes creating a plane of cleavage. For example, slate is a metamorphic rock, originating from shale
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Igneous rock
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Igneous rock, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava, the magma can be derived from partial melts of existing rocks in either a planets mantle or crust. Typically, the melting is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks, Igneous and metamorphic rocks make up 90–95% of the top 16 km of the Earths crust by volume. Igneous rocks form about 15% of the Earths current land surface, most of the Earths oceanic crust is made of igneous rock. In terms of modes of occurrence, igneous rocks can be either intrusive or extrusive, the mineral grains in such rocks can generally be identified with the naked eye. Intrusive rocks can also be classified according to the shape and size of the intrusive body, typical intrusive formations are batholiths, stocks, laccoliths, sills and dikes. When the magma solidifies within the earths crust, it cools slowly forming coarse textured rocks, such as granite, gabbro, the central cores of major mountain ranges consist of intrusive igneous rocks, usually granite. When exposed by erosion, these cores may occupy huge areas of the Earths surface, intrusive igneous rocks that form at depth within the crust are termed plutonic rocks and are usually coarse-grained. Intrusive igneous rocks that form near the surface are termed subvolcanic or hypabyssal rocks, hypabyssal rocks are less common than plutonic or volcanic rocks and often form dikes, sills, laccoliths, lopoliths, or phacoliths. Extrusive igneous rocks, also known as rocks, are formed at the crusts surface as a result of the partial melting of rocks within the mantle. Extrusive igneous rocks cool and solidify quicker than intrusive igneous rocks and they are formed by the cooling of molten magma on the earths surface. The magma, which is brought to the surface through fissures or volcanic eruptions, hence such rocks are smooth, crystalline and fine-grained. Basalt is an extrusive igneous rock and forms lava flows, lava sheets. Some kinds of basalt solidify to form long polygonal columns, the Giants Causeway in Antrim, Northern Ireland is an example. The molten rock, with or without suspended crystals and gas bubbles, is called magma and it rises because it is less dense than the rock from which it was created. When magma reaches the surface from beneath water or air, it is called lava, eruptions of volcanoes into air are termed subaerial, whereas those occurring underneath the ocean are termed submarine. Black smokers and mid-ocean ridge basalt are examples of volcanic activity
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Layered intrusion
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A layered intrusion is a large sill-like body of igneous rock which exhibits vertical layering or differences in composition and texture. These intrusions typically are many kilometres in area covering from around 100 km2 to over 50,000 km2, while most are Archean to Proterozoic in age they may be any age such as the Cenozoic Skaergaard intrusion of east Greenland or the Rum layered intrusion in Scotland. Although most are ultramafic to mafic in composition, the Ilimaussaq complex of Greenland is an alkalic intrusion, layered intrusions are found in typically ancient cratons and are rare but worldwide in distribution. The intrusive complexes exhibit evidence of fractional crystallization and crystal segregation by settling or floating of minerals from a melt, some include diorite and granophyre near the top of the bodies. Orebodies of platinum group elements, chromite, magnetite and ilmenite are often associated with these rare intrusions, mafic-ultramafic layered intrusions occur at all levels within the crust, from depths in excess of 50 km to depths of as little as 1.5 to 5 km. The depth at which an intrusion is formed is dependent on several factors, magmas with high magnesium and iron contents are denser and are therefore less likely to be able to reach the surface. As an ascending magma rises and cools, it becomes thicker and this then restricts the magma from rising further because more energy is required to push it upwards. Conversely, thicker magma is more efficient at forcing apart the wall rocks. It is difficult to determine what causes large ultramafic – mafic intrusives to be emplaced within the crust. For instance, in most Archaean cratons, greenstone belts correlate with voluminous dyke injection as well as some form of larger intrusive episodes into the crust. This is particularly true of a series of ultramafic-mafic layered intrusions in the Yilgarn Craton of ~2.8 Ga and associated komatiite volcanism, plume magmatism is an effective mechanism for explaining the large volumes of magmatism required to inflate an intrusion to several kilometres thickness. Plumes also tend to create warping of the crust, weaken it thermally so that it is easier to intrude magma, the presence of large layered complexes in Greenland such as the Skaergaard intrusion which is not related to mantle plumes indicate other processes can form these intrusions. Here, the large volumes which are created by mid-ocean ridge spreading allow the accumulation of large volumes of cumulate rocks. Plume magmatism is supported in some intrusions by geochemistry, in particular the Norilsk-Talnakh intrusions are considered to be created by plume magmatism and other large intrusions have been suggested as created by mantle plumes. The causes of layering in large ultramafic intrusions include convection, thermal diffusion, settling of phenocrysts, assimilation of wall rocks, the primary mechanism for forming cumulate layers is of course the accumulation of layers of mineral crystals on the floor or roof of the intrusion. Rarely, plagioclase is found in layers at the top of intrusions. Here it can form anorthosite layers, accumulation occurs as crystals are formed by fractional crystallisation and, if they are dense enough, precipitate out from the magma. The Skaergaard intrusion in Greenland is an example of these quasi-sedimentary structures
40.
Cumulate rock
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Cumulate rocks are igneous rocks formed by the accumulation of crystals from a magma either by settling or floating. Cumulate rocks are named according to their texture, cumulate texture is diagnostic of the conditions of formation of group of igneous rocks. Cumulate rocks are the product of precipitation of solid crystals from a fractionating magma chamber. These accumulations typically occur on the floor of the magma chamber, cumulates are typically found in ultramafic intrusions, in the base of large ultramafic lava tubes in komatiite and magnesium rich basalt flows and also in some granitic intrusions. Cumulates are named according to their dominant mineralogy and the percentage of crystals to their groundmass, adcumulates are rocks containing ~100–93% accumulated magmatic crystals in a fine-grained groundmass. Mesocumulates are rocks with between 93 and 85% accumulated minerals in a groundmass, orthocumulates are rocks containing between 85 and 75% accumulated minerals in groundmass. Cumulate rocks are named according to the cumulate minerals in order of abundance, and then cumulate type. For example, a layer with 50% plagioclase, 40% pyroxene, 5% olivine, a rock consisting of 80% olivine, 5% magnetite and 15% groundmass is an olivine mesocumulate. Cumulate terminology is appropriate for use when describing cumulate rocks, in intrusions which have a uniform composition and minimal textural and mineralogical layering or visible crystal accumulations it is inappropriate to describe them according to this convention. Cumulate rocks, because they are fractionates of a parental magma, the chemistry of the cumulate itself can inform on the residual melt composition, but several factors need to be considered. In this example, the precipitation of anorthite removes calcium from the melt, enstatite being precipitated from the melt will remove magnesium, so the melt becomes depleted in these elements. This tends to enrich the concentration of other elements - typically sodium, potassium, titanium, the rock that is made of the accumulated minerals will not have the same composition as the magma. In the above example, the cumulate of anorthite + enstatite is rich in calcium and magnesium, the cumulate rock is a plagioclase-pyroxene cumulate and the melt is now more felsic and aluminous in composition. In the above example, the plagioclase and pyroxene need not be pure end-member compositions, the minerals can be precipitated in any ratio within the cumulate, such cumulates can be 90% plagioclase, 10% enstatite, through to 10% plagiclase, 90% enstatite and remain a gabbro. This also alters the chemistry of the cumulate, and the depletions of the residual melt, in nature, cumulates usually form from 2 mineral species, although ranges from 1 to 4 mineral species are known. Cumulate rocks which are formed from one mineral alone are often named after the mineral, a specific example is the Skaergaard intrusion in Greenland. One way to infer the composition of the magma that created the cumulate rocks is to measure groundmass chemistry, otherwise, complex calculations of averaging cumulate layers must be utilised, which is a complex process. Alternatively, the composition can be estimated by assuming certain conditions of magma chemistry
41.
Pyroxenite
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Pyroxenite is an ultramafic igneous rock consisting essentially of minerals of the pyroxene group, such as augite, diopside, hypersthene, bronzite or enstatite. Pyroxenites are classified into clinopyroxenites, orthopyroxenites, and the websterites which contain both types of pyroxenes, closely allied to this group are the hornblendites, consisting essentially of hornblende and other amphiboles. They are essentially of igneous origin, though some pyroxenites are included in the metamorphic Lewisian complex of Scotland and this connection is indicated also by their mode of occurrence, for they usually accompany masses of gabbro and peridotite and seldom are found by themselves. They are often very coarse-grained, containing individual crystals which may be several inches in length, the principal accessory minerals, in addition to olivine and feldspar, are chromite and other spinels, garnet, magnetite, rutile, and scapolite. Pyroxenites can be formed as cumulates in ultramafic intrusions by accumulation of crystals at the base of the magma chamber. Here they are associated with gabbro and anorthite cumulate layers and are typically high up in the intrusion. They may be accompanied by layers, ilmenite layers. Pyroxenites are also found as layers within masses of peridotite and these layers most commonly have been interpreted as products of reaction between ascending magmas and peridotite of the upper mantle. The layers typically are a few centimeters to a meter or so in thickness, pyroxenites that occur as xenoliths in basalt and in kimberlite have been interpreted as fragments of such layers. Although some mantle pyroxenites contain garnet, they are not eclogites, as clinopyroxene in them is less sodic than omphacite, purely pyroxene-bearing volcanic rocks are rare, restricted to spinifex-textured sills, lava tubes and thick flows in the Archaean greenstone belts. This is in similar to the formation of olivine spinifex textures in komatiite lava flows. They frequently occur in the form of dikes or segregations in gabbro and peridotite, in Shetland, Cortland on the Hudson River, North Carolina, Baltimore, New Zealand and they are also found in the Bushveld Igneous Complex in South Africa and Zimbabwe. The pyroxenites are often subject serpentinization under low temperature retrograde metamorphism, under pressure-metamorphism hornblende is developed and various types of amphibolite and hornblende-schist are produced. Sobolev, A. V. and others,2007, The amount of recycled crust in sources of mantle-derived melts, Science 316, media related to Pyroxenite at Wikimedia Commons Flett, John Smith
42.
Magnesium
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Magnesium is a chemical element with symbol Mg and atomic number 12. Magnesium is the ninth most abundant element in the universe and it is produced in large, aging stars from the sequential addition of three helium nuclei to a carbon nucleus. When such stars explode as supernovas, much of the magnesium is expelled into the medium where it may recycle into new star systems. Magnesium is the eighth most abundant element in the Earths crust and the fourth most common element in the Earth, making up 13% of the planets mass and it is the third most abundant element dissolved in seawater, after sodium and chlorine. Magnesium occurs naturally only in combination with elements, where it invariably has a +2 oxidation state. The free element can be produced artificially, and is highly reactive, the free metal burns with a characteristic brilliant-white light. The metal is now obtained mainly by electrolysis of magnesium salts obtained from brine, Magnesium is less dense than aluminium, and the alloy is prized for its combination of lightness and strength. Magnesium is the eleventh most abundant element by mass in the body and is essential to all cells. Magnesium ions interact with polyphosphate compounds such as ATP, DNA, hundreds of enzymes require magnesium ions to function. Magnesium compounds are used medicinally as common laxatives, antacids, elemental magnesium is a gray-white lightweight metal, two-thirds the density of aluminium. Magnesium has the lowest melting and the lowest boiling point 1,363 K of all the alkaline earth metals, Magnesium reacts with water at room temperature, though it reacts much more slowly than calcium, a similar group 2 metal. When submerged in water, hydrogen bubbles form slowly on the surface of the metal—though, if powdered, the reaction occurs faster with higher temperatures. Magnesiums reversible reaction with water can be harnessed to store energy, Magnesium also reacts exothermically with most acids such as hydrochloric acid, producing the metal chloride and hydrogen gas, similar to the HCl reaction with aluminium, zinc, and many other metals. Magnesium is highly flammable, especially when powdered or shaved into thin strips, flame temperatures of magnesium and magnesium alloys can reach 3,100 °C, although flame height above the burning metal is usually less than 300 mm. Once ignited, such fires are difficult to extinguish, with combustion continuing in nitrogen, carbon dioxide, Magnesium may also be used as an igniter for thermite, a mixture of aluminium and iron oxide powder that ignites only at a very high temperature. When burning in air, magnesium produces a light that includes strong ultraviolet wavelengths. Magnesium powder was used for illumination in the early days of photography. Later, magnesium filament was used in electrically ignited single-use photography flashbulbs, Magnesium powder is used in fireworks and marine flares where a brilliant white light is required
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Mica
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The mica group of sheet silicate minerals includes several closely related materials having nearly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition, the nearly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms. The word mica is derived from the Latin word mica, meaning a crumb, and probably influenced by micare, to glitter. Chemically, micas can be given the general formula X2Y4–6Z8O204 in which X is K, Na, or Ca or less commonly Ba, Rb, or Cs, Y is Al, Mg, or Fe or less commonly Mn, Cr, Ti, Li, etc. Z is chiefly Si or Al, but also may include Fe3+ or Ti, structurally, micas can be classed as dioctahedral and trioctahedral. If the X ion is K or Na, the mica is a common mica, whereas if the X ion is Ca, mica is widely distributed and occurs in igneous, metamorphic and sedimentary regimes. Large crystals of mica used for various applications are typically mined from granitic pegmatites, until the 19th century, large crystals of mica were quite rare and expensive as a result of the limited supply in Europe. However, their price dramatically dropped when large reserves were found and mined in Africa, the largest documented single crystal of mica was found in Lacey Mine, Ontario, Canada, it measured 10 ×4.3 ×4.3 m and weighed about 330 tonnes. Similar-sized crystals were found in Karelia, Russia. The British Geological Survey reported that as of 2005, Koderma district in Jharkhand state in India had the largest deposits of mica in the world. China was the top producer of mica with almost a third of the share, closely followed by the US, South Korea. Large deposits of mica were mined in New England from the 19th century to the 1970s. Large mines existed in Connecticut, New Hampshire, and Maine, scrap and flake mica is produced all over the world. In 2010, the producers were Russia, Finland, United States, South Korea, France. The total production was 350,000 t, although no data were available for China. Most sheet mica was produced in India and Russia, flake mica comes from several sources, the metamorphic rock called schist as a byproduct of processing feldspar and kaolin resources, from placer deposits, and from pegmatites. Sheet mica is considerably less abundant than flake and scrap mica, the most important sources of sheet mica are pegmatite deposits. Sheet mica prices vary with grade and can range from less than $1 per kilogram for low-quality mica to more than $2,000 per kilogram for the highest quality, the mica group represents 37 phyllosilicate minerals that have a layered or platy texture
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Amphibole
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Amphiboles can be green, black, colorless, white, yellow, blue, or brown. The International Mineralogical Association currently classifies amphiboles as a mineral supergroup, amphiboles crystallize into two crystal systems, monoclinic and orthorhombic. In chemical composition and general characteristics they are similar to the pyroxenes, the chief differences from pyroxenes are that amphiboles contain essential hydroxyl or halogen and the basic structure is a double chain of tetrahedra. Most apparent, in specimens, is that amphiboles form oblique cleavage planes. Amphiboles are also less dense than the corresponding pyroxenes. In optical characteristics, many amphiboles are distinguished by their stronger pleochroism, amphiboles are the primary constituent of amphibolites. Amphiboles are minerals of either igneous or metamorphic origin, in the former case occurring as constituents of rocks, such as granite, diorite, andesite. Calcium is sometimes a constituent of naturally occurring amphiboles and those of metamorphic origin include examples such as those developed in limestones by contact metamorphism and those formed by the alteration of other ferromagnesian minerals. Pseudomorphs of amphibole after pyroxene are known as uralite, the name amphibole was used by René Just Haüy to include tremolite, actinolite, tourmaline and hornblende. The group was so named by Haüy in allusion to the variety, in composition and appearance. This term has since applied to the whole group. Numerous sub-species and varieties are distinguished, the important of which are tabulated below in two series. The formulae of each will be seen to be built on the general double-chain silicate formula RSi4O11, four of the amphibole minerals are among the minerals commonly called asbestos. These are, anthophyllite, riebeckite, cummingtonite/grunerite series, and actinolite/tremolite series, the cummingtonite/grunerite series is often termed amosite or brown asbestos, riebeckite is known as crocidolite or blue asbestos. These are generally called amphibole asbestos, anthophyllite occurs as brownish, fibrous or lamellar masses with hornblende in mica-schist at Kongsberg in Norway and some other localities. An aluminous related species is known as gedrite and a deep green Russian variety containing little iron as kupfferite, hornblende is an important constituent of many igneous rocks. It is also an important constituent of amphibolites formed by metamorphism of basalt, actinolite is an important and common member of the monoclinic series, forming radiating groups of acicular crystals of a bright green or greyish-green color. It occurs frequently as a constituent of greenschists, the name is a translation of the old German word Strahlstein
45.
Rutile
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Rutile is a mineral composed primarily of titanium dioxide, TiO2. Rutile is the most common form of TiO2. Three rarer polymorphs of TiO2 are known, Anatase, a metastable tetragonal mineral of pseudo-octahedral habit Brookite, an orthorhombic mineral TiO2, rutile has among the highest refractive indices at visible wavelengths of any known crystal, and also exhibits a particularly large birefringence and high dispersion. Owing to these properties, it is useful for the manufacture of optical elements, especially polarization optics, for longer visible. Natural rutile may contain up to 10% iron and significant amounts of niobium and tantalum, rutile derives its name from the Latin rutilus, red, in reference to the deep red color observed in some specimens when viewed by transmitted light. Rutile is an accessory mineral in high-temperature and high-pressure metamorphic rocks. Thermodynamically, rutile is the most stable polymorph of TiO2 at all temperatures, consequently, the transformation of the metastable TiO2 polymorphs to rutile is irreversible. As it has the lowest molecular volume of the three polymorphs, it is generally the primary titanium bearing phase in most high-pressure metamorphic rocks. The occurrence of large specimen crystals is most common in pegmatites, skarns, rutile is found as an accessory mineral in some altered igneous rocks, and in certain gneisses and schists. In groups of acicular crystals it is frequently seen penetrating quartz as in the fléches damour from Graubünden, in 2005 the Republic of Sierra Leone in West Africa had a production capacity of 23% of the worlds annual rutile supply, which rose to approximately 30% in 2008. The reserves, lasting for about 19 years, are estimated at 259,000,000 metric tons, rutile has a body-centred tetragonal unit cell, with unit cell parameters a=b=4.584 Å, and c=2.953 Å. The titanium cations have a number of 6 meaning they are surrounded by an octahedron of 6 oxygen atoms. The oxygen anions have a number of 3 resulting in a trigonal planar co-ordination. Rutile also shows a screw axis when its octahedra are viewed sequentially, rutile crystals are most commonly observed to exhibit a prsimatic or acicular growth habit with preferential orientation along their c-axis, the direction. This growth habit is favored as the facets of rutile exhibit the lowest surface free energy and are therefore thermodynamically most stable, the c-axis oriented growth of rutile appears clearly in nanorods, nanowires and Abnormal grain growth phenomena of this phase. In large enough quantities in beach sands, rutile forms an important constituent of heavy minerals, miners extract and separate the valuable minerals—e. g. The main uses for rutile are the manufacture of ceramic, as a pigment. Finely powdered rutile is a brilliant white pigment and is used in paints, plastics, paper, foods, titanium dioxide pigment is the single greatest use of titanium worldwide
