Offretite Mineral Data

General Offretite Information

Chemical Formula:

(K2,Ca,Mg)2.5Al5Si13O36•15(H2O)

Composition:

Molecular Weight = 1,453.72 gm

Potassium 2.96 % K 3.56 % K₂O

Calcium 3.03 % Ca 4.24 % CaO

Magnesium 1.17 % Mg 1.94 % MgO

Aluminum 9.65 % Al 18.24 % Al₂O₃

Silicon 24.73 % Si 52.90 % SiO₂

Hydrogen 2.11 % H 18.84 % H₂O

Oxygen 56.35 % O

______ ______

100.00 % 99.72 % = TOTAL OXIDE

Empirical Formula:

K_1.1Ca_1.1Mg_0.7Al_5.2Si_12.8O₃₆•15.2(H₂O)

Environment:

Alteration of basalt with the addition of potash.

IMA Status:

Valid Species (Pre-IMA) 1890

Locality:

Mont Simiouse, near Montbrison, Loire, France. Link to MinDat.org Location Data.

Name Origin:

Named for Albert Jules Joseph Offret (1857-?), professor in the Faculty of Sciences, Lyon, France.

Name Pronunciation:

Offretite + Pronunciation

Synonym:

ICSD 8292

PDF 25-1186

Offretite Image

Images:

Offretite

Comments: Clear crystal of offretite on matrix.
Location: Mont Simiouse, near Montbrison, Loire, France. Scale: Not Given.
© Lou Perloff / Photo Atlas of Minerals

Offretite Crystallography

Axial Ratios:

a:c = 1:0.57052

Cell Dimensions:

a = 13.307, c = 7.592, Z = 1; V = 1,164.25 Den(Calc)= 2.07

Crystal System:

Hexagonal - Ditrigonal Dipyramidal H-M Symbol (6 m2) Space Group: P 6m2

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

By Intensity(I/I_o): 11.5(1), 2.88(0.65), 4.35(0.6),

Physical Properties of Offretite

Cleavage:

{0001} Distinct

Color:

Colorless, White.

Density:

2.13

Diaphaneity:

Transparent to Translucent

Fracture:

Brittle - Uneven - Very brittle fracture producing uneven fragments.

Habit:

Hexagonal - Six-sided crystal shape in cross-section or habit.

Habit:

Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline).

Habit:

Radial - Crystals radiate from a center without producing stellar forms (e.g. stibnite)

Hardness:

4-4.5 - Between Fluorite and Apatite

Luster:

Vitreous (Glassy)

Streak:

white

Optical Properties of Offretite

Gladstone-Dale:

CI meas= 0.006 (Superior) - where the CI = (1-KPDmeas/KC)
CI calc= -0.023 (Excellent) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.237,KPDmeas= 0.2303,KC= 0.2316
Ncalc = 1.48 - 1.49

Optical Data:

Uniaxial (-), e=1.486-1.492, w=1.489-1.495, bire=0.0030.

Calculated Properties of Offretite

Electron Density:

Bulk Density (Electron Density)=2.16 gm/cc
note: Specific Gravity of Offretite =2.13 gm/cc.

Fermion Index:

Fermion Index = 0.01
Boson Index = 0.99

Photoelectric:

PE_Offretite= 1.96 barns/electron
U=PE_Offretite x r_electron= 4.24 barns/cc.

Radioactivity:

GRapi = 43.33 (Gamma Ray American Petroleum Institute Units)
Concentration of Offretite per GRapi unit = 2.31 (%)

Estimated Radioactivity from Offretite - barely detectable

Offretite Classification

Dana Class:

77.01.02.04 (77)Tectosilicate Zeolite group

(77.01)true zeolites

(77.01.02)Chabazite and related species

77.01.02.01 Chabazite-Ca (Ca0.5,Na,K)4[Al4Si8O24]•12H2O P1 1

77.01.02.01a Chabazite-Na! (Na2,K2,Ca,Mg)[Al2Si4O12]•6(H2O) R 3m 3 2/m

77.01.02.01b Chabazite-K! (K2,Ca,Na2,Mg)[Al2Si4O12]•6(H2O) R 3m 3 2/m

77.01.02.01c Chabazite-Sr! (Sr,Ca,K2,Na2)[Al2Si4O12]•6(H2O) R 3m 3 2/m

77.01.02.02 Herschelite? (Na,Ca,K)AlSi2O6•3(H2O) R 3m 3 2/m

77.01.02.03 Willhendersonite KCaAl3Si3O12•5(H2O) P1 1

77.01.02.04 Offretite (K2,Ca,Mg)2.5Al5Si13O36•15(H2O) P 6m2 6 m2

77.01.02.05 Erionite-Na (Na2,K2,Ca)2[Al4Si14O36]•15(H2O) P 6₃/mmc 6/m 2/m 2/m

77.01.02.05a Erionite-K! (K2,Ca,Na2)2[Al4Si14O36]•15(H2O) P 6₃/mmc 6/m 2/m 2/m

77.01.02.05b Erionite-Ca! (Ca,K2,Na2)2[Al4Si14O36]•15(H2O) P 6₃/mmc 6/m 2/m 2/m

77.01.02.06 Gmelinite-Na (Na2,Ca)Al2Si4O12•6(H2O) P 6₃/mmc 6/m 2/m 2/m

77.01.02.06a Gmelinite-Ca! (Ca,Na2)Al2Si4O12•6(H2O) P 6₃/mmc 6/m 2/m 2/m

77.01.02.06b Gmelinite-K! (K,Na,Ca)6(Al7Si17O48)•22(H2O) P 6₃/mmc 6/m 2/m 2/m

77.01.02.07 Faujasite-Na (Na2,Ca,Mg)3.5[Al7Si17O48]•32(H2O) F d3m 4/m 3 2/m

77.01.02.07a Faujasite-Ca! (Ca,Na2,Mg)3.5[Al7Si17O48]•32(H2O) F d3m 4/m 3 2/m

77.01.02.07b Faujasite-Mg! (Mg,Na2,Ca)3.5[Al7Si17O48]•32(H2O) F d3m 4/m 3 2/m

77.01.02.08 Levyne-Ca (Ca,Na2,K2)Al2Si4O12•6(H2O) R 3m 3 2/m

77.01.02.08a Levyne-Na! (Na2,Ca,K2)Al2Si4O12•6(H2O) R 3m 3 2/m

77.01.02.09 Tschortnerite! Ca4(Ca,Sr,K,Ba)3Cu3(OH)8[Si12Al12O48]•x(H2O),x>=20 F m3m 4/m 3 2/m

Strunz Class:

09.GD.25 09 - SILICATES (Germanates)

09.G - Tektosilicates with Zeolitic H2O

09.GD -Chains of 6-membered rings ï¿½ tabular zeolites

09.GD.25 Offretite (K2,Ca,Mg)2.5Al5Si13O36•15(H2O) P 6m2 6 m2

09.GD.25 Wenkite Ba4Ca6(Si,Al)20O39(OH)2(SO4)3•n(H2O)(?) P 62m 6 m2

Other Offretite Information

References:

NAME( Ford32) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(AntBidBlaNic2)

See Also:

Links to other databases for Offretite :
1 - Am. Min. Crystal Structure Database
2 - Athena
3 - EUROmin Project
4 - Ecole des Mines de Paris
5 - GeoScienceWorld
6 - Google Images
7 - Google Scholar
8 - Handbook of Mineralogy (MinSocAm)
9 - Handbook of Mineralogy (UofA)
10 - MinDAT
11 - Mineralienatlas (Deutsch)
12 - Online Mineral Museum
13 - QUT Mineral Atlas
14 - Ruff.Info
15 - WWW-MINCRYST
16 - Zeolite Database by Bruno Herreros

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Offretite

(K2,Ca,Mg)2.5Al5Si13O36•15(H2O)
Dana No: 77.01.02.04 Strunz No: 09.GD.25
Locality:

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