Gypsum Mineral Data

Gypsum Mineral Data +

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General Gypsum Information

Chemical Formula:

CaSO4·2(H2O)

Composition:

Molecular Weight = 172.17 gm

Calcium 23.28 % Ca 32.57 % CaO

Hydrogen 2.34 % H 20.93 % H₂O

Sulfur 18.62 % S 46.50 % SO₃

Oxygen 55.76 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

Ca(SO₄)·2(H₂O)

Environment:

Sedimentary evaporite deposits.

IMA Status:

Valid Species (Pre-IMA) Prehistoric

Locality:

Numerous localities worldwide. Naica, Chihuahua, Mexico. Link to MinDat.org Location Data.

Name Origin:

From the Greek, gyps meaning "burned" mineral. Selenite from the Greek in allusion to its pearly luster (moon light) on cleavage fragments.

Synonym:

Alabaster

ICSD 2057

PDF 33-311

Satin Spar

Selenite

Gypsum Image

Images:

Gypsum

Comments: Bladed rosettes of gypsum.
Location: unknown. Scale: Specimen size 6 cm.
© Dave Barthelmy

Images:

Gypsum

Comments: Pencil-sized acicular crystals of gypsum.
Location: Naica, Chihuahua, S.A., Mexico. Scale: Specimen size 5 cm.
© Dave Barthelmy

Gypsum Crystallography

Axial Ratios:

a:b:c =0.3741:1:0.4143

Cell Dimensions:

a = 5.68, b = 15.18, c = 6.29, Z = 4; beta = 113.833° V = 496.09 Den(Calc)= 2.31

Crystal System:

Monoclinic - PrismaticH-M Symbol (2/m) Space Group: A2/a

$Help on X Ray Diffraction:$ X Ray Diffraction:

By Intensity(I/I_o): 7.63(1), 4.28(1), 3.07(0.8),2.87(0.5), 2.69(0.4), 2.09(0.3), 2.22(0.2), 3.8(0.2),

Forms:

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Forms: [ 0 1 0] [ 1 1 1] [ 1 2 0]

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Crystal Structure:

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Schofield P F , Knight K S , Stretton I C , American Mineralogist , 81 (1996) p.847-851, Thermal expansion of gypsum investigated by neutron powder diffraction, T = 4.2 K

View Additional jPOWD Structure files for Gypsum
[1] [2] [3]

Physical Properties of Gypsum

Cleavage:

[010] Perfect, [100] Distinct, [011] Distinct

Color:

White, Colorless, Yellowish white, Greenish white, Brown.

Density:

2.3

Diaphaniety:

Transparent to translucent

Fracture:

Fibrous - Thin, elongated fractures produced by crystal forms or intersecting cleavages (e.g. asbestos).

Habit:

Crystalline - Coarse - Occurs as well-formed coarse sized crystals.

Habit:

Massive - Fibrous - Distinctly fibrous fine-grained forms.

Habit:

Tabular - Form dimensions are thin in one direction.

Hardness:

2 - Gypsum

Luminescence:

None.

Luster:

Pearly

Streak:

white

Optical Properties of Gypsum

Gladstone-Dale:

CI meas= -0.027 (Excellent) - where the CI = (1-KPDmeas/KC)
CI calc= -0.022 (Excellent) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2268,KPDmeas= 0.2278,KC= 0.2219

Optical Data:

Biaxial (+), a=1.519-1.521, b=1.522-1.523, g=1.529-1.53, bire=0.0090-0.0100, 2V(Calc)=58-68, 2V(Meas)=58. Dispersion strong, r > v.

Pleochroism (x):

colorless.

Pleochroism (y):

colorless.

Pleochroism (z):

colorless.

Calculated Properties of Gypsum

Electron Density:

r_electron=2.36 gm/cc
note: r_Gypsum=2.31 gm/cc.

Fermion Index

Fermion Index = 0.00198
Boson Index = 0.99802

Photoelectric:

PE_Gypsum= 3.97 barns/electron
U=PE_Gypsum x r_electron= 9.37 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Gypsum is Not Radioactive

Gypsum Classification

Dana Class:

29.6.3.1 (29)Hydrated Acid and Sulfates

(29.6)where A XO4 · x(H2O)

(29.6.3)Dana Group

29.6.3.1 Gypsum CaSO4·2(H2O) A2/a 2/m

Strunz Class:

VI/C.22-20 VI - Sulfates,Chromates,Molybdates and Tungstates

VI/C - Water-bearing sulfates without unfamiliar anions. Cations of very big size

VI/C.22 - Bassanite - Ardealite series

VI/C.22-10 Bassanite 2CaSO4·(H2O) Unk Ortho

VI/C.22-20 Gypsum CaSO4·2(H2O) A2/a 2/m

VI/C.22-25 Rapidcreekite Ca2(SO4)(CO3)·4(H2O) Pcnb 2/m 2/m 2/m

VI/C.22-30 Ardealite Ca2(SO4)(HPO4)·4(H2O) Cc m

Other Gypsum Information

References:

NAME( ODonoghue90) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(Heinrich65)

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Gypsum

CaSO4·2(H2O)
Dana No: 29.6.3.1 Strunz No: VI/C.22-20
Locality:

Notes: