Specific gravity is the ratio of the density of a substance to the density of a reference substance. 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 for liquids is nearly always water at its densest. Nonetheless, the temperature and pressure must be specified for 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 1,000. Specific gravity is used in industry as a simple means of obtaining information about the concentration of solutions of various materials such as brines, antifreeze coolants, sugar solutions and acids. Being a ratio of densities, specific gravity is a dimensionless quantity; the reason for the specific gravity being dimensionless is to provide a global consistency between the U. S. and Metric Systems, since various units for density may be used such as pounds per cubic feet or grams per cubic centimeter, etc.
Specific gravity varies with pressure. Substances with a specific gravity of 1 are neutrally buoyant in water; those with SG greater than 1 are denser than water and will, disregarding surface tension effects, sink in it. Those with an SG less than 1 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 for historical reasons. True specific gravity can be expressed mathematically as: S G true = ρ sample ρ H 2 O where ρsample is the density of the sample and ρH2O is the density of water; the apparent specific gravity is the ratio of the weights of equal volumes of sample and water in air: S G apparent = W A, sample W A, H 2 O where WA,sample represents the weight of the sample measured in air and WA,H2O the weight of water measured in air. It can be shown that true specific gravity can be computed from different properties: S G true = ρ sample ρ H 2 O = m sample V m H 2 O V = m sample m H 2 O g g = W V, sample W V, H 2 O where g is the local acceleration due to gravity, V is the volume of the sample and of water, ρsample is the density of the sample, ρH2O is the density of water and WV represents a weight obtained in vacuum.
The density of water varies with 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, it is nearly always the case. But as specific gravity refers to incompressible aqueous solutions or other incompressible substances, variations in density caused by pressure are neglected at least where apparent specific gravity is being measured. For true specific gravity calculations, air pressure must be considered. Temperatures are specified by the notation, with Ts representing the temperature at which the sample's density was determined and Tr 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 SGH2O = 1.000000, it is the case that SGH2O = 0.998203⁄0.999840 = 0.998363. Here, temperature is being specified using the current ITS-90 scale and the densities used here and in the rest of this article are based on that scale.
On the previous IPTS-68 scale, the densities at 20 °C and 4 °C are 0.9982071 and 0.9999720 respective
Mohs scale of mineral hardness
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, some of which are more quantitative; the method of comparing hardness by observing which minerals can scratch others is of great antiquity, having been mentioned by Theophrastus in his treatise On Stones, c. 300 BC, followed by Pliny the Elder in his Naturalis Historia, c. 77 AD. While 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 relevant for field geologists, who use the scale to identify minerals using scratch kits; the Mohs scale hardness of minerals can be found in reference sheets. Mohs hardness is useful in milling, it allows assessment of.
The scale is used at electronic manufacturers for testing the resilience of flat panel display components. 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 chemically pure solids found in nature. Rocks are made up of one or more minerals; as the hardest known 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 given material can scratch, or the softest material that can scratch the given material. For example, if some material is scratched by apatite but not by fluorite, its hardness on the Mohs scale would fall between 4 and 5. "Scratching" a material for the purposes of the Mohs scale means creating non-elastic dislocations visible to the naked eye. Materials that are lower on the Mohs scale can create microscopic, non-elastic dislocations on materials that have a higher Mohs number.
While these microscopic dislocations are permanent and sometimes detrimental to the harder material's structural integrity, they are not considered "scratches" for the determination of a Mohs scale number. The Mohs scale is a purely 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. Cordua, William S. "The Hardness of Minerals and Rocks". Lapidary Digest, c. 1990
In mineralogy, crystal habit is the characteristic external shape of an individual crystal or crystal group. A single crystal's habit is a description of its general shape and its crystallographic forms, plus how well developed each form is. 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 developed faces is subhedral, one with undeveloped crystal faces is called anhedral. The long axis of a euhedral quartz crystal 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 grow in a fibrous habit, a mass of fine fibers; 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. Euhedral crystals formed in uncrowded conditions with no adjacent crystal grains are not common. Factors influencing habit include: a combination of two or more crystal forms. Minerals belonging to the same crystal system do not 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, those found in Montana form stout tabular crystals. Ordinarily, the latter habit is seen only in ruby. Sapphire and ruby are both varieties of the same mineral: corundum; some minerals may replace other existing minerals while preserving the original's habit: this process is called pseudomorphous replacement. A classic example is tiger's eye quartz, crocidolite asbestos replaced by silica. While quartz forms prismatic crystals, in tiger's eye the original fibrous habit of crocidolite is preserved; the names of crystal habits are derived from: Predominant crystal faces.
Crystal forms. Aggregation of crystals or aggregates. Crystal appearance. Abnormal grain growth Grain growth
The sulfide minerals are a class of minerals containing sulfide as the major anion. Some sulfide minerals are economically important as metal ores; the sulfide class includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, the sulfarsenides and the sulfosalts. Sulfide minerals are inorganic compounds. Common or important examples include: Acanthite Ag2S Chalcocite Cu2S Bornite Cu5FeS4 Galena PbS Sphalerite ZnS Chalcopyrite CuFeS2 Pyrrhotite Fe1−xS Millerite NiS Pentlandite 9S8 Covellite CuS Cinnabar HgS Realgar AsS Orpiment As2S3 Stibnite Sb2S3 Pyrite FeS2 Marcasite FeS2 Molybdenite MoS2Sulfarsenides: Cobaltite AsS Arsenopyrite FeAsS Gersdorffite NiAsSSulfosalts: Pyrargyrite Ag3SbS3 Proustite Ag3AsS3 Tetrahedrite Cu12Sb4S13 Tennantite Cu12As4S13 Enargite Cu3AsS4 Bournonite PbCuSbS3 Jamesonite Pb4FeSb6S14 Cylindrite Pb3Sn4FeSb2S14 IMA-CNMNC proposes a new hierarchical scheme; this list uses the Classification of Nickel–Strunz. Abbreviations: "*" - discredited.
"?" - questionable/doubtful. "REE" - Rare-earth element "PGE" - Platinum-group element 03. C Aluminofluorides, 06 Borates, 08 Vanadates, 09 Silicates: Neso: insular Soro: grouping Cyclo: ring Ino: chain Phyllo: sheet Tekto: three-dimensional framework Nickel–Strunz code scheme: NN. XY.##x NN: Nickel–Strunz mineral class number X: Nickel–Strunz mineral division letter Y: Nickel–Strunz mineral family letter ##x: Nickel–Strunz mineral/group number, x add-on letter 02. A Simple Sulfides, etc. 02. AA Alloys of metalloids with Cu, Ag, Sn, Au: 10a Algodonite, 10b Domeykite, 10d Koutekite. AB Ni-metalloid alloys: 10 Orcelite, 15 Maucherite, 20 Oregonite 02. AC Alloys of metalloids with PGE: 05a Atheneite, 05a Vincentite. B Metal Sulfides, M:S > 1:1 02. BA With Cu, Ag, Au: 05a Chalcocite, 05b Djurleite, 05c Geerite, 05d Roxbyite, 05e Digenite, 05f Anilite. BB With Ni, Fe: 05 Heazlewoodite. BC With Rh, Pd, Pt, etc.: 05 Palladseite, 05 Miassite. BD With Hg, Tl: 05 Imiterite, 10 Gortdrumite. BE With Pb: 05 Betekhtinite, 10 Furutobeite.
C Metal Sulfides, M:S = 1:1 02. CA With Cu: 05a Covellite, 05b Klockmannite, 05c Spionkopite, 05d Yarrowite. CB With Zn, Fe, Cu, Ag, Au, etc.: 05a Rudashevskyite, 05a Hawleyite, 05a Coloradoite, 05a Metacinnabar, 05a Sphalerite, 05a Tiemannite, 05a Stilleite, 05b Sakuraiite, 05c Polhemusite. CC With Ni, Fe, Co, PGE, etc.: 05 Zlatogorite, 05 Breithauptite, 05 Freboldite, 05 Langisite, 05 Nickeline, 05 Sederholmite, 05 Stumpflite, 05 Sudburyite, 05 Sobolevskite, 05 Achavalite, 05 Jaipurite*, 05 Hexatestibiopanickelite, 05 Kotulskite. CD With Sn, Pb, Hg, etc.: 05 Herzenbergite, 05 Teallite.
Monoclinic crystal system
In crystallography, the monoclinic crystal system is one of the 7 crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic system, they form a rectangular prism with a parallelogram as its base. Hence two vectors are perpendicular, while the third vector meets the other two at an angle other than 90°. There is only one monoclinic Bravais lattice in two dimensions: the oblique lattice. Two monoclinic Bravais lattices exist: the primitive monoclinic and the base-centered monoclinic lattices. In the monoclinic system there is a used second choice of crystal axes that results in a unit cell with the shape of an oblique rhombic prism. In this axis setting, the primitive and base-centered lattices swap in centering type; the table below organizes the space groups of the monoclinic crystal system by crystal class. It lists the International Tables for Crystallography space group numbers, followed by the crystal class name, its point group in Schoenflies notation, Hermann–Mauguin notation, orbifold notation, Coxeter notation, type descriptors, mineral examples, the notation for the space groups.
Sphenoidal is monoclinic hemimorphic. The three monoclinic hemimorphic space groups are as follows: a prism with as cross-section wallpaper group p2 ditto with screw axes instead of axes ditto with screw axes as well as axes, parallel, in between; the four monoclinic hemihedral space groups include those with pure reflection at the base of the prism and halfway those with glide planes instead of pure reflection planes. Crystal structure Crystallography Crystal Hurlbut, Cornelius S.. Manual of Mineralogy. Pp. 69–73. ISBN 0-471-80580-7. Hahn, Theo, ed.. International Tables for Crystallography, Volume A: Space Group Symmetry. A. Berlin, New York: Springer-Verlag. Doi:10.1107/97809553602060000100. ISBN 978-0-7923-6590-7
In the field of mineralogy, fracture is the texture and shape of a rock's surface formed when a mineral is fractured. Minerals have a distinctive fracture, making it a principal feature used in their identification. Fracture differs from cleavage in that the latter involves clean splitting along the cleavage planes of the mineral's crystal structure, as opposed to more general breakage. All minerals exhibit fracture, but when strong cleavage is present, it can be difficult to see. Conchoidal fracture breakage that resembles the concentric ripples of a mussel shell, it occurs in amorphous or fine-grained minerals such as flint, opal or obsidian, but may occur in crystalline minerals such as quartz. Subconchoidal fracture is similar to with less significant curvature. Earthy fracture is reminiscent of freshly broken soil, it is seen in soft, loosely bound minerals, such as limonite and aluminite. Hackly fracture is jagged and not even, it occurs when metals are torn, so is encountered in native metals such as copper and silver.
Splintery fracture comprises sharp elongated points. It is seen in fibrous minerals such as chrysotile, but may occur in non-fibrous minerals such as kyanite. Uneven fracture is a rough one with random irregularities, it occurs in a wide range of minerals including arsenopyrite and magnetite. Rudolf Duda and Lubos Rejl: Minerals of the World http://www.galleries.com/minerals/property/fracture.htm