Polyhalite Mineral Data

Polyhalite Mineral Data +

General Polyhalite Information

Chemical Formula:

K2Ca2Mg(SO4)4·2(H2O)

Composition:

Molecular Weight = 602.94 gm

Potassium 12.97 % K 15.62 % K₂O

Calcium 13.29 % Ca 18.60 % CaO

Magnesium 4.03 % Mg 6.68 % MgO

Hydrogen 0.67 % H 5.98 % H₂O

Sulfur 21.27 % S 53.12 % SO₃

Oxygen 47.76 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

K₂Ca₂Mg(SO₄)₄·2(H₂O)

Environment:

Sedimentary marine evaporite deposits.

IMA Status:

Valid Species (Pre-IMA) 1818

Locality:

Potash beds near Carlsbad, New Mexico. Link to MinDat.org Location Data.

Name Origin:

From the Greek, polys, meaning "much" and hals, meaning "salt." in allusion to the many salt components in the formulae..

Synonym:

ICSD 6303

PDF 21-982

Polyhalite Image

Images:

Polyhalite

Comments: White crystals of polyhalite in matrix.
Location: Ronneburg U deposit, Gera district, Thuringia, Germany. Scale: Picture size 1.5 mm.
© Thomas Witzke / Abraxas-Verlag

Polyhalite Crystallography

Axial Ratios:

a:b:c =0.7158:1:0.4654

Cell Dimensions:

a = 11.69, b = 16.33, c = 7.6, Z = 4; alpha = 91.6°, beta = 90°, gamma = 91.9° V = 1,449.46 Den(Calc)= 2.76

Crystal System:

TriclinicSpace Group: P 1,P1

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

By Intensity(I/I_o): 2.9(1), 3.18(0.7), 2.85(0.16),

Forms:

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Forms: [ 0 1 0] [ 1 3 1] [ 1 1 0] [ 1 0 0] [ 0 0 1]

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Crystal Structure:

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Bindi L , Acta Crystallographica, Section E , 61 (2005) p.i135-i136, Reinvestigation of the crystal structure of polyhalite, K2Ca2Mg(SO4)4*2H2O

View Additional jPOWD Structure files for Polyhalite
[1]

Physical Properties of Polyhalite

Cleavage:

[101] Perfect

Color:

Colorless, Gray, Gray white, White, Pink.

Density:

2.77 - 2.78, Average = 2.77

Diaphaniety:

Transparent to Translucent

Fracture:

Brittle - Conchoidal - Very brittle fracture producing small, conchoidal fragments.

Habit:

Massive - Fibrous - Distinctly fibrous fine-grained forms.

Habit:

Massive - Lamellar - Distinctly foliated fine-grained forms.

Hardness:

2.5-3.5 - Finger Nail-Copper Penny

Luster:

Vitreous (Glassy)

Streak:

white

Optical Properties of Polyhalite

Gladstone-Dale:

CI meas= -0.019 (Superior) - where the CI = (1-KPDmeas/KC)
CI calc= -0.024 (Excellent) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2022,KPDmeas= 0.2011,KC= 0.1974

Optical Data:

Biaxial (-), a=1.546-1.548, b=1.558-1.562, g=1.567, bire=0.0190-0.0210, 2V(Calc)=60-80, 2V(Meas)=60-62.

Pleochroism (x):

colorless.

Pleochroism (y):

colorless.

Pleochroism (z):

colorless.

Calculated Properties of Polyhalite

Electron Density:

r_electron=2.78 gm/cc
note: r_Polyhalite=2.78 gm/cc.

Fermion Index

Fermion Index = 0.00605
Boson Index = 0.99395

Photoelectric:

PE_Polyhalite= 4.30 barns/electron
U=PE_Polyhalite x r_electron= 11.94 barns/cc.

Radioactivity:

GRapi = 187.47 (Gamma Ray American Petroleum Institute Units)

Estimated Radioactivity from Polyhalite - barely detectable

Polyhalite Classification

Dana Class:

29.4.5.1 (29)Hydrated Acid and Sulfates

(29.4)where (A+)2 Bn (XO4)p · x(H2O)

(29.4.5)Dana Group

29.4.5.1 Polyhalite K2Ca2Mg(SO4)4·2(H2O) P 1,P1 Tri

29.4.5.2 Leightonite K2Ca2Cu(SO4)4·2(H2O) C 2/c 2/m

Strunz Class:

VI/C.20-10 VI - Sulfates,Chromates,Molybdates and Tungstates

VI/C - Water-bearing sulfates without unfamiliar anions. cations of medium and very big size

VI/C.20 - Polyhalite - Görgeyite series

VI/C.20-10 Polyhalite K2Ca2Mg(SO4)4·2(H2O) P 1,P1 Tri

VI/C.20-20 Leightonite K2Ca2Cu(SO4)4·2(H2O) C 2/c 2/m

VI/C.20-30 Gorgeyite K2Ca5(SO4)6·(H2O) C 2/c 2/m

Other Polyhalite Information

References:

NAME( Duda&Rejl90) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(Ford32)

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Polyhalite

K2Ca2Mg(SO4)4·2(H2O)
Dana No: 29.4.5.1 Strunz No: VI/C.20-10
Locality:

Notes: