Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the microscope and to the naked eye. Cleavage forms parallel to crystallographic planes: Basal or pinacoidal cleavage occurs when there is only one cleavage plane. Graphite has basal cleavage. Mica has basal cleavage. Cubic cleavage occurs on. Halite has cubic cleavage, therefore, when halite crystals are broken, they will form more cubes. Octahedral cleavage occurs. Fluorite exhibits perfect octahedral cleavage. Octahedral cleavage is common for semiconductors. Diamond has octahedral cleavage. Rhombohedral cleavage occurs when there are three cleavage planes intersecting at angles that are not 90 degrees. Calcite has rhombohedral cleavage. Prismatic cleavage occurs. Spodumene exhibits prismatic cleavage. Dodecahedral cleavage occurs.
Sphalerite has dodecahedral cleavage. Crystal parting occurs when minerals break along planes of structural weakness due to external stress or along twin composition planes. Parting breaks are similar in appearance to cleavage, but only occur due to stress. Examples include magnetite which shows octahedral parting, the rhombohedral parting of corundum and basal parting in pyroxenes. Cleavage is a physical 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 prismatic cleavage planes for the pyroxenes and the amphiboles are diagnostic. Crystal cleavage is of technical importance in the electronics industry and in the cutting of gemstones. Precious stones are cleaved by impact, as in diamond cutting. Synthetic single crystals of semiconductor materials are sold as thin wafers which are much easier to cleave. Pressing a silicon wafer against a soft surface and scratching its edge with a diamond scribe is enough to cause cleavage.
Elemental semiconductors are a space group for which octahedral cleavage is observed. This means. Most other commercial semiconductors can be made in the related zinc blende structure, with similar cleavage planes. Cleavage Mineral galleries: Mineral properties – Cleavage
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury. In English, Mars carries a name of the Roman god of war, is referred to as the "Red Planet" because the reddish iron oxide prevalent on its surface gives it a reddish appearance, distinctive among the astronomical bodies visible to the naked eye. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys and polar ice caps of Earth; the days and seasons are comparable to those of Earth, because the rotational period as well as the tilt of the rotational axis relative to the ecliptic plane are similar. Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, of Valles Marineris, one of the largest canyons in the Solar System; the smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature. Mars has two moons and Deimos, which are small and irregularly shaped.
These may be captured asteroids, similar to a Mars trojan. There are ongoing investigations assessing the past habitability potential of Mars, as well as the possibility of extant life. Future astrobiology missions are planned, including the Mars 2020 and ExoMars rovers. Liquid water cannot exist on the surface of Mars due to low atmospheric pressure, less than 1% of the Earth's, except at the lowest elevations for short periods; the two polar ice caps appear to be made of water. The volume of water ice in the south polar ice cap, if melted, would be sufficient to cover the entire planetary surface to a depth of 11 meters. In November 2016, NASA reported finding a large amount of underground ice in the Utopia Planitia region of Mars; the volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior. Mars can be seen from Earth with the naked eye, as can its reddish coloring, its apparent magnitude reaches −2.94, surpassed only by Jupiter, the Moon, the Sun.
Optical ground-based telescopes are limited to resolving features about 300 kilometers across when Earth and Mars are closest because of Earth's atmosphere. Mars is half the diameter of Earth with a surface area only less than the total area of Earth's dry land. Mars is less dense than Earth, having about 15% of Earth's volume and 11% of Earth's mass, resulting in about 38% of Earth's surface gravity; the red-orange appearance of the Martian surface is caused by rust. It can look like butterscotch. Like Earth, Mars has differentiated into a dense metallic core overlaid by less dense materials. Current models of its interior imply a core with a radius of about 1,794 ± 65 kilometers, consisting of iron and nickel with about 16–17% sulfur; this iron sulfide core is thought to be twice as rich in lighter elements as Earth's. The core is surrounded by a silicate mantle that formed many of the tectonic and volcanic features on the planet, but it appears to be dormant. Besides silicon and oxygen, the most abundant elements in the Martian crust are iron, aluminum and potassium.
The average thickness of the planet's crust is about 50 km, with a maximum thickness of 125 km. Earth's crust averages 40 km. Mars is a terrestrial planet that consists of minerals containing silicon and oxygen and other elements that make up rock; the surface of Mars is composed of tholeiitic basalt, although parts are more silica-rich than typical basalt and may be similar to andesitic rocks on Earth or silica glass. Regions of low albedo suggest concentrations of plagioclase feldspar, with northern low albedo regions displaying higher than normal concentrations of sheet silicates and high-silicon glass. Parts of the southern highlands include detectable amounts of high-calcium pyroxenes. Localized concentrations of hematite and olivine have been found. Much of the surface is covered by finely grained iron oxide dust. Although Mars has no evidence of a structured global magnetic field, observations show that parts of the planet's crust have been magnetized, suggesting that alternating polarity reversals of its dipole field have occurred in the past.
This paleomagnetism of magnetically susceptible minerals is similar to the alternating bands found on Earth's ocean floors. One theory, published in 1999 and re-examined in October 2005, is that these bands suggest plate tectonic activity on Mars four billion years ago, before the planetary dynamo ceased to function and the planet's magnetic field faded, it is thought that, during the Solar System's formation, Mars was created as the result of a stochastic process of run-away accretion of material from the protoplanetary disk that orbited the Sun. Mars has many distinctive chemical features caused by its position in the Solar System. Elements with comparatively low boiling points, such as chlorine and sulphur, are much more common on Mars than Earth. After the formation of the planets, all were subjected to the so-called "Late Heavy Bombardment". About 60% of the surface of Mars shows a record of impacts from that era, whereas much of the remaining surface is underlain by immense impact basins caused by those events.
There is evidence of an enormous impact basin in the northern hemisphere of Mars, spanning 10,600 by 8,500 km, or four times the size of the Moon's South Pole – Aitk
Extinction (optical mineralogy)
Extinction is a term used in optical mineralogy and petrology, which describes when cross-polarized light dims, as viewed through a thin section of a mineral in a petrographic microscope. Isotropic minerals, opaque minerals, or amorphous materials show no light. Anisotropic minerals will show one extinction for each 90 degrees of stage rotation; the extinction angle is the measure between the cleavage direction or habit of a mineral and the extinction. To find this line up the cleavage lines/long direction with one of the crosshairs in the microscope, turn the mineral until the extinction occurs; the number of degrees the stage was rotated is the extinction angle, between 0-89 degrees. 90 degrees would be considered zero degrees, is known as parallel extinction. Inclined extinction is a measured angle between 1-89 degrees. Minerals with two cleavages can have two extinction angles, with symmetrical extinction occurring when minerals have multiple angles that are the same. Minerals that have no cleavage or elongation can not have an extinction angle.
Minerals with undulose extinction, solid solution/zonation, or other factors that may inhibit this measure and may be more difficult to use. Nesse, W. D.. Introduction to Optical Mineralogy. New York: Oxford University Press. P. 335. ISBN 0-19-506024-5
Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up 90 percent of the Earth's crust. In mineralogy, silica SiO2 is considered a silicate mineral. Silica is found in nature as the mineral quartz, its polymorphs. On Earth, a wide variety of silicate minerals occur in an wider range of combinations as a result of the processes that have been forming and re-working the crust for billions of years; these processes include partial melting, fractionation, metamorphism and diagenesis. Living organisms contribute to this geologic cycle. For example, a type of plankton known as diatoms construct their exoskeletons from silica extracted from seawater; the tests of dead diatoms are a major constituent of deep ocean sediment, of diatomaceous earth. A silicate mineral is an ionic compound whose anions consist predominantly of silicon and oxygen atoms. In most minerals in the Earth's crust, each silicon atom is the center of an ideal tetrahedron, whose corners are four oxygen atoms covalently bound to it.
Two adjacent tetrahedra may share a vertex, meaning that the oxygen atom is a bridge connecting the two silicon atoms. An unpaired vertex represents an ionized oxygen atom, covalently bound to a single silicon atom, that contributes one unit of negative charge to the anion; some silicon centers may be replaced by atoms of other elements, still bound to the four corner oxygen corners. If the substituted atom is not tetravalent, it contributes extra charge to the anion, which requires extra cations. For example, in the mineral orthoclase n, the anion is a tridimensional network of tetrahedra in which all oxygen corners are shared. If all tetrahedra had silicon centers, the anion would be just neutral silica n. Replacement of one every four silicon atoms by an aluminum atom results in the anion n, whose charge is neutralized by the potassium cations K+. In mineralogy, silicate minerals are classified into seven major groups according to the structure of their silicate anion: Note that tectosilicates can only have additional cations if some of the silicon is replaced by an atom of lower valence such as aluminium.
Al for Si substitution is common. Nesosilicates, or orthosilicates, have the orthosilicate ion, which constitute isolated 4− tetrahedra that are connected only by interstitial cations; the Nickel–Strunz classification is 09. A –examples include: Phenakite group Phenakite – Be2SiO4 Willemite – Zn2SiO4 Olivine group Forsterite – Mg2SiO4 Fayalite – Fe2SiO4 Tephroite – Mn2SiO4 Garnet group Pyrope – Mg3Al23 Almandine – Fe3Al23 Spessartine – Mn3Al23 Grossular – Ca3Al23 Andradite – Ca3Fe23 Uvarovite – Ca3Cr23 Hydrogrossular – Ca3Al2Si2O83−m4m Zircon group Zircon – ZrSiO4 Thorite – SiO4 Hafnon – SiO4 Al2SiO5 group Andalusite – Al2SiO5 Kyanite – Al2SiO5 Sillimanite – Al2SiO5 Dumortierite – Al6.5–7BO333 Topaz – Al2SiO42 Staurolite – Fe2Al942 Humite group – 732Norbergite – Mg32 Chondrodite – Mg522 Humite – Mg732 Clinohumite – Mg942 Datolite – CaBSiO4 Titanite – CaTiSiO5 Chloritoid – 2Al4Si2O104 Mullite – Al6Si2O13 Sorosilicates have isolated pyrosilicate anions Si2O6−7, consisting of double tetrahedra with a shared oxygen vertex—a silicon:oxygen ratio of 2:7.
The Nickel–Strunz classification is 09. B. Examples include: Hemimorphite – Zn42·H2O Lawsonite – CaAl22·H2O Axinite – 3Al2 Ilvaite – CaFeII2FeIIIO Epidote group Epidote – Ca23O Zoisite – Ca2Al3O Tanzanite – Ca2Al3O Clinozoisite – Ca2Al3O Allanite – CaAl2O Dollaseite- – CaCeMg2AlSi3O11F Vesuvianite – Ca102Al4524 Cyclosilicates, or ring silicates, have three or more tetrahedra linked in a ring; the general formula is 2x−, where one or more silicon atoms can be replaced by other 4-coordinated atom. The silicon:oxygen ratio is 1:3. Double rings have the formula 2x−; the Nickel–Strunz classification is 09. C. Possible ring sizes include: Some example minerals are: 3-member single ring Benitoite – BaTi 4-member single ring Papagoite – CaCuAlSi2O63. 6-member single ring Beryl – Be3Al2 Bazzite – Be3Sc2 Sugilite – KNa22Li3Si12O30 Tourmaline – 3−634 Pezzottaite – CsAl2Si6O18 Osumilite – 2312O30 Cordierite – 2Al4Si5O18 Sekaninaite – 2Al4Si5O18 9-member single ring Eudialyte – Na15Ca63Zr3SiO3222 6-member double ring Milarite – K2Ca4Al2Be4H2ONote that the ring in axinite contains two B and four Si tetrahedra and is distorted compared to the other 6-member ring cyclosilicates.
Inosilicates, or chain silicates, have interlocking chains of silicate tetrahedra with either SiO3, 1:3 ratio, for single chains or Si4O11, 4:11 ratio, for double chains. The Nickel–Strunz classification is 09. D – examples include: Pyroxene group Enstatite – orthoferrosilite series Enstatite – MgSiO3 Ferrosilite – FeSiO3 Pigeonite – Ca0.251.75Si2O6 Diopside – hedenbergite series Diopside – CaMgSi2O6 Hedenbergite – CaFeSi2O6 Augite – 2O6 Sodium pyroxene series Jadeite – NaAlSi2O6 Aegirine (or ac
A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnified image of an object. This is opposed to a macrograph or photomacrograph, an image, taken on a microscope but is only magnified less than 10 times. Micrography is the art of using microscopes to make photographs. A micrograph contains extensive details of microstructure. A wealth of information can be obtained from a simple micrograph like behavior of the material under different conditions, the phases found in the system, failure analysis, grain size estimation, elemental analysis and so on. Micrographs are used in all fields of microscopy. A light micrograph or photomicrograph is a micrograph prepared using an optical microscope, a process referred to as photomicroscopy. At a basic level, photomicroscopy may be performed by connecting a camera to a microscope, thereby enabling the user to take photographs at reasonably high magnification. Scientific use began in England in 1850 by Prof Richard Hill Norris FRSE for his studies of blood cells.
Roman Vishniac was a pioneer in the field of photomicroscopy, specializing in the photography of living creatures in full motion. He made major developments in light-interruption photography and color photomicroscopy. Photomicrographs may be obtained using a USB microscope attached directly to a home computer or laptop. An electron micrograph is a micrograph prepared using an electron microscope. Micrographs have micron bars, or magnification ratios, or both. Magnification is a ratio between the size of an object on its real size. Magnification can be a misleading parameter as it depends on the final size of a printed picture and therefore varies with picture size. A scale bar, or micron bar, is a line of known length displayed on a picture; the bar can be used for measurements on a picture. When the picture is resized the bar is resized making it possible to recalculate the magnification. Ideally, all pictures destined for publication/presentation should be supplied with a scale bar. All but one of the micrographs presented on this page do not have a micron bar.
The microscope has been used for scientific discovery. It has been linked to the arts since its invention in the 17th century. Early adopters of the microscope, such as Robert Hooke and Antonie van Leeuwenhoek, were excellent illustrators. After the invention of photography in the 1820s the microscope was combined with the camera to take pictures instead of relying on an artistic rendering. Since the early 1970s individuals have been using the microscope as an artistic instrument. Websites and traveling art exhibits such as the Nikon Small World and Olympus Bioscapes have featured a range of images for the sole purpose of artistic enjoyment; some collaborative groups, such as the Paper Project have incorporated microscopic imagery into tactile art pieces as well as 3D immersive rooms and dance performances. Close-up Digital microscope Macro photography Microphotograph Microscopy USB microscope Make a Micrograph – This presentation by the research department of Children's Hospital Boston shows how researchers create a three-color micrograph.
Shots with a Microscope – a basic, comprehensive guide to photomicrography Scientific photomicrographs – free scientific quality photomicrographs by Doc. RNDr. Josef Reischig, CSc. Micrographs of 18 natural fibres by the International Year of Natural Fibres 2009 Seeing Beyond the Human Eye Video produced by Off Book - Solomon C. Fuller bio Charles Krebs Microscopic Images Dennis Kunkel Microscopy Andrew Paul Leonard, APL Microscopic Cell Centered Database - Montage Nikon Small World Olympus Bioscapes Other examples
In optical mineralogy and petrography, a thin section is a laboratory preparation of a rock, soil, bones, or metal sample for use with a polarizing petrographic microscope, electron microscope and electron microprobe. A thin sliver of rock is cut from the sample with a diamond ground optically flat, it is mounted on a glass slide and ground smooth using progressively finer abrasive grit until the sample is only 30 μm thick. The method involved using the Michel-Lévy interference colour chart. Quartz is used as the gauge to determine thickness as it is one of the most abundant minerals; when placed between two polarizing filters set at right angles to each other, the optical properties of the minerals in the thin section alter the colour and intensity of the light as seen by the viewer. As different minerals have different optical properties, most rock forming minerals can be identified. Plagioclase for example can be seen in the photo on the right as a clear mineral with multiple parallel twinning planes.
The large blue-green minerals are clinopyroxene with some exsolution of orthopyroxene. Thin sections are prepared in order to investigate the optical properties of the minerals in the rock; this work helps to reveal the origin and evolution of the parent rock. A photograph of a rock in thin section is referred to as a photomicrograph. Under thin section, in plane polarized light, quartz is colorless with no cleavage, its habit is either equant or anhedral if it infills around other minerals as a cement. Under cross polarized light quartz displays low interference colors and is the defining mineral used to determine if the thin section is at standardized thickness of 30 microns as quartz will only display up to a pale yellow interference color and no further at that thickness, it is common in most rocks so it will be available to judge the thickness. In thin section, quartz grain provenance in a sedimentary rock can be estimated. In crossed polarized light, the quartz grain can go extinct all at once, called monocrystalline quartz, or in waves, called polycrystalline quartz.
The extinction in waves is called undulose extinction and indicates dislocation walls in mineral grains. Dislocation walls are where dislocations, intracrystalline deformation via movement of a dislocation front within a plane, organize themselves into planes of sufficient quantity, they change the crystallographic orientation across the walls, so for example in quartz, the two sides of the wall will have different extinction angles and thus result in undulose extinction. Since undulose extinction requires dislocation walls to have developed, these occur more at higher pressures and temperatures, quartz grains with undulose extinction indicate metamorphic rock provenance for that grain; those grains that are monocrystalline quartz are more to have been formed by igneous processes. Differing sources suggest the extent; some note the trend for immature sandstones to have less polycrystalline quartz grains compared to mature sandstones, which have grains that have passed through many sedimentary cycles.
Quartz grains derived from previous sedimentary sources are determined by looking for authigenic, or grown in place, overgrowths of silica cement over the grain. The above descriptions of quartz in thin section is enough to identify it. Minerals with similar appearance may include plagioclase, although it can be distinguished by the distinctive twinning in crossed polarized light and cleavage in plane polarized light, cordierite, although it can be distinguished by twinning or inclusions in the grain. However, for certainty, other distinguishing features of quartz include the fact that it is uniaxial, it has a positive optic sign, length-slow sign of elongation, zero degree extinction angle. Fine-grained rocks those containing minerals of high birefringence, such as calcite, are sometimes prepared as ultra-thin sections. An ordinary 30 μm thin section is prepared as described above but the slice of rock is attached to the glass slide using a soluble cement such as Canada balsam to allow both sides to be worked on.
The section is polished on both sides using a fine diamond paste until it has a thickness in the range of 2-12 μm. This technique has been used to study the microstructure of fine-grained carbonates such as the Lochseitenkalk mylonite in which the matrix grains are less than 5 μm in size; this method is sometimes used in the preparation of mineral and rock specimens for transmission electron microscopy and allows greater accuracy in comparing features using both optical and electron imaging. Ceramography: thin sections of ceramics Shelley, D. Optical Mineralogy, Second Edition. University of Canterbury, New Zealand. Thin sections of soils. Collection of Prof. Kubiëna
In mathematics and chemistry, a space group is the symmetry group of a configuration in space in three dimensions. In three dimensions, there are 230 if chiral copies are considered distinct. Space groups are studied in dimensions other than 3 where they are sometimes called Bieberbach groups, are discrete cocompact groups of isometries of an oriented Euclidean space. In crystallography, space groups are called the crystallographic or Fedorov groups, represent a description of the symmetry of the crystal. A definitive source regarding 3-dimensional space groups is the International Tables for Crystallography. Space groups in 2 dimensions are the 17 wallpaper groups which have been known for several centuries, though the proof that the list was complete was only given in 1891, after the much more difficult classification of space groups had been completed. In 1879 Leonhard Sohncke listed the 65 space groups. More he listed 66 groups, but Fedorov and Schönflies both noticed that two of them were the same.
The space groups in three dimensions were first enumerated by Fedorov, shortly afterwards were independently enumerated by Schönflies. The correct list of 230 space groups was found by 1892 during correspondence between Fedorov and Schönflies. Barlow enumerated the groups with a different method, but omitted four groups though he had the correct list of 230 groups from 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, each of the latter belonging to one of 7 lattice systems. This results in a space group being some combination of the translational symmetry of a unit cell including lattice centering, the point group symmetry operations of reflection and improper rotation, the screw axis and glide plane symmetry operations; 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 the identity element, reflections and improper rotations. 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, one of the 32 possible point groups. Translation is defined as the face moves from one point to another point. A glide plane is a reflection in a plane, followed by a translation parallel with that plane; this is noted depending on which axis the glide is along. There is the n glide, a glide along the half of a diagonal of a face, the d glide, a fourth of the way along either a face or space diagonal of the unit cell; the latter is called the diamond glide plane. In 17 space groups, due to the centering of the cell, the glides occur in two perpendicular directions i.e. the same glide plane can be called b or c, a or b, a or c. For example, group Abm2 could be called Acm2, group Ccca could be called Cccb.
In 1992, it was suggested to use symbol e for such planes. The symbols for five space groups have been modified: A screw axis is a rotation about an axis, followed by a translation along the direction of the axis; these are noted by a number, n, to describe the degree of rotation, where the number is how many operations must be applied to complete a full rotation. The degree of translation is 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 twofold rotation followed by a translation of 1/2 of the lattice vector; the general formula for the action of an element of a space group is y = M.x + D where M is its matrix, D is its vector, where the element transforms point x into point y. In general, D = D + D, where D is a unique function of M, zero for M being the identity; the matrices M form a point group, a basis of the space group. The lattice dimension can be less than the overall dimension, resulting in a "subperiodic" space group.
For:: One-dimensional line groups: Two-dimensional line groups: frieze groups: Wallpaper groups: Three-dimensional line groups. Some of these methods can assign several different names to the same space group, so altogether there are many thousands of different names. Number; the International Union of Crystallography publishes tables of all space group types, assigns each a unique number from 1 to 230. The numbering is arbitrary, except that groups with the same crystal system or point group are given consecutive numbers. International symbol or Hermann–Mauguin notation; the Hermann–Mauguin notation describes the lattice and some generators for the group. It has a shortened form called the international short symbol, the one most used in crystallography