монета - ohmen und mahren 1943

Twin Buttes, Pima County, Arizona, USA 67

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Locality: synthetic. Zeitschrift fur Kristallographie 217:9-10.

Ichharam V V H (2002) Redetermination of the crystal structure of calcium sulphate dihydrate, CaSO4*2H2O

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Gypsum no.101 - Goldschmidt (1913-1926)

Gypsum no.52 - Goldschmidt (1913-1926)

Gypsum no.36 - Goldschmidt (1913-1926)

Gypsum no.23 - Goldschmidt (1913-1926)

Gypsum no.4 - Goldschmidt (1913-1926)

Found as both massive material, including the alabaster variety; and clear crystals, the selenite variety; and, parallel fibrous, the satin spar variety. Typically colourless to white, transparent crystals, thick tabular to lenticular, sometimes prismatic.Visit gemdat.org for . Currently in public beta-test. Classification of Gypsum Valid - first described prior to 1959 (pre-IMA) - "Grandfathered" 6/C.22-20 7.CD.407 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)C : Sulfates (selenates, etc.) without additional anions, with H2OD : With only large cationsDana 7th edition ID:29.6.3.1 29.6.3.129 : HYDRATED ACID AND NORMAL SULFATES6 : AXO4·xH2O 25.4.325 : Sulphates4 : Sulphates of Ca, Sr and Bamindat.org URL: Please feel free to link to this page.Occurrences of GypsumGeological Setting:Commonest of the sulphate minerals, gypsum is found in marine evaporites, in caves where the air is dry enough to allow it to be deposited and remain, at fumaroles, and in the oxidized zones of sulfide deposits on occasion.Physical Properties of Gypsum Vitreous, Sub-Vitreous, Silky, Pearly, DullDiaphaneity (Transparency):Transparent, Translucent, OpaqueComment:Wide range of luster based on varieties, pearly on {010}Colour:Colourless to white, often tinged other hues due to impurities; colourless in transmitted light..Streak:White.Hardness (Mohs):2Hardness Data:Mohs hardness reference speciesComment:Hardness varies with direction down to 1.5Tenacity:FlexibleCleavage:PerfectPerfect (eminent) and easy on {010}, almost micaceous in some samples; on {100} distinct, yielding a surface with a conchoidal fracture; on {011}, yielding a fibrous fracture {001}.Fracture:Splintery, ConchoidalTranslation gliding:Readily undergroes translation gliding with T{010}, t{[001], which can also be generated by torsion about [001], or bending {010} about [010].Comment:Also inelastic. Breakage depends on orientation.Density (measured):2.312 - 2.322 g/cm3Density (calculated):2.308 g/cm3Crystallography of GypsumCrystal System:MonoclinicClass (H-M):2/m - PrismaticCell Parameters:a = 5.679(5) Г , b = 15.202(14) Г , c = 6.522(6) Г β = 118.43°Ratio:a:b:c = 0.374 : 1 : 0.429Unit Cell Volume:V 495.15 Г В (Calculated from Unit Cell)Z:4Morphology:Thin to thick tabular crystals, {010} with {111} and {120}; also prismatic [001], stout to acicular, with the prism zone often striated. Crystals may have warped surfaces, or be bent or twisted. Rosette-like clusters of lenticular crystals are common. Also found as granular masses, massive beds, and fibrous masses ("satin spar"). Twinning:{100} ("swallow-tail"), very common, with a re-entrant angle formed ordinarily by {111}; on {101} as contact twins ("butterfly" or "heart-shaped"), along {111}; on {209}; also as cruciform penetration twins.Comment:Data for I2/c cell (non-standard setting). There is another setting with space group C2/c and beta ~ 127В`, and a further C2/c setting with a ~6.27, b ~15.20, c ~5.67 A, beta ~114В`.Crystal Atlas:

Formula:CaSO 4 · 2H 2OSystem:MonoclinicColour:Colourless to white, ...Hardness:2Name:Named in antiquity from the Greek "gypsos," meaning plaster.Isostructural with: The most common sulphate mineral.

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