Offretite Mineral Data

Offretite Mineral Data +

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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.

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 DipyramidalH-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),

Crystal Structure:

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Gualtieri A , Artioli G , Passaglia E , Bigi S , Viani A , Hanson J C , American Mineralogist , 83 (1998) p.590-606, Crystal structure-crystal chemistry relationships in the zeolites erionite, and offretite, Sample from Mt. Semiol

View Additional jPOWD Structure files for Offretite
[1] [2]

Physical Properties of Offretite

Cleavage:

[0001] Distinct

Color:

Colorless, White.

Density:

2.13

Diaphaniety:

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

Optical Data:

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

Calculated Properties of Offretite

Electron Density:

r_electron=2.16 gm/cc
note: r_Offretite=2.13 gm/cc.

Fermion Index

Fermion Index = 0.01303
Boson Index = 0.98697

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)

Estimated Radioactivity from Offretite - barely detectable

Offretite Classification

Dana Class:

77.1.2.4 (77)Tectosilicate Zeolite group

(77.1)true zeolites

(77.1.2)Chabazite and related species

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

77.1.2.1a Chabazite-Na! (Na2,K2,Ca,Mg)[Al2Si4O12]·6(H2O) R 3m 3 2/m

77.1.2.1b Chabazite-K! (K2,Ca,Na2,Mg)[Al2Si4O12]·6(H2O) R 3m 3 2/m

77.1.2.1c Chabazite-Sr! (Sr,Ca,K2,Na2)[Al2Si4O12]·6(H2O) R 3m 3 2/m

77.1.2.2 Herschelite? (Na,Ca,K)AlSi2O6·3(H2O) R 3m 3 2/m

77.1.2.3 Willhendersonite KCaAl3Si3O12·5(H2O) P1 1

77.1.2.4 Offretite (K2,Ca,Mg)2.5Al5Si13O36·15(H2O) P 6m2 6 m2

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

77.1.2.5a Erionite-K! (K2,Ca,Na2)2[Al4Si14O36]·15(H2O) P 6₃/mmc 6/m 2/m 2/m

77.1.2.5b Erionite-Ca! (Ca,K2,Na2)2[Al4Si14O36]·15(H2O) P 6₃/mmc 6/m 2/m 2/m

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

77.1.2.6a Gmelinite-Ca! (Ca,Na2)Al2Si4O12·6(H2O) P 6₃/mmc 6/m 2/m 2/m

77.1.2.6b Gmelinite-K! (K,Na,Ca)6(Al7Si17O48)·22(H2O) P 6₃/mmc 6/m 2/m 2/m

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

77.1.2.7a Faujasite-Ca! (Ca,Na2,Mg)3.5[Al7Si17O48]·32(H2O) F d3m 4/m 3 2/m

77.1.2.7b Faujasite-Mg! (Mg,Na2,Ca)3.5[Al7Si17O48]·32(H2O) F d3m 4/m 3 2/m

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

77.1.2.8a Levyne-Na! (Na2,Ca,K2)Al2Si4O12·6(H2O) R 3m 3 2/m

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

Strunz Class:

VIII/J.26-70 VIII - Silicates

VIII/J - Tectosilicates (network), with zeolite-structure, Bladed Zeolites

VIII/J.26 - Zeolite group, Willhendersonite - Chabazite - Perialite series

VIII/J.26-10 Willhendersonite KCaAl3Si3O12·5(H2O) P1 1

VIII/J.26-20 Chabazite-Na! (Na2,K2,Ca,Mg)[Al2Si4O12]·6(H2O) R 3m 3 2/m

VIII/J.26-25 Chabazite-K! (K2,Ca,Na2,Mg)[Al2Si4O12]·6(H2O) R 3m 3 2/m

VIII/J.26-30 Chabazite-Ca (Ca0.5,Na,K)4[Al4Si8O24]·12H2O P1 1

VIII/J.26-35 Chabazite-Sr! (Sr,Ca,K2,Na2)[Al2Si4O12]·6(H2O) R 3m 3 2/m

VIII/J.26-40 Tschernichite (Ca,Na)(Si6Al2)O16·4-8(H2O) P 4/mmm 4/m 2/m 2/m

VIII/J.26-50 Gmelinite-Na (Na2,Ca)Al2Si4O12·6(H2O) P 6₃/mmc 6/m 2/m 2/m

VIII/J.26-52 Gmelinite-K! (K,Na,Ca)6(Al7Si17O48)·22(H2O) P 6₃/mmc 6/m 2/m 2/m

VIII/J.26-54 Gmelinite-Ca! (Ca,Na2)Al2Si4O12·6(H2O) P 6₃/mmc 6/m 2/m 2/m

VIII/J.26-58 Levyne-Na! (Na2,Ca,K2)Al2Si4O12·6(H2O) R 3m 3 2/m

VIII/J.26-60 Levyne-Ca (Ca,Na2,K2)Al2Si4O12·6(H2O) R 3m 3 2/m

VIII/J.26-70 Offretite (K2,Ca,Mg)2.5Al5Si13O36·15(H2O) P 6m2 6 m2

VIII/J.26-80 Mazzite K2CaMg2(Al,Si)36O72·28(H2O) P 6₃/mmc 6/m 2/m 2/m

VIII/J.26-90 Erionite-Na (Na2,K2,Ca)2[Al4Si14O36]·15(H2O) P 6₃/mmc 6/m 2/m 2/m

VIII/J.26-92 Erionite-K! (K2,Ca,Na2)2[Al4Si14O36]·15(H2O) P 6₃/mmc 6/m 2/m 2/m

VIII/J.26-94 Erionite-Ca! (Ca,K2,Na2)2[Al4Si14O36]·15(H2O) P 6₃/mmc 6/m 2/m 2/m

VIII/J.26-95 Bellbergite (K,Ba,Sr)2Sr2Ca2(Ca,Na)4Al18Si18O72·30(H2O) P 6₃/mmc, P 6₂c-, P 6₃mc Hex

VIII/J.26-100 Perlialite K8Tl4Al12Si24O72·20(H2O) P 6/mmm 6/m 2/m 2/m

Other Offretite Information

References:

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

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Offretite

(K2,Ca,Mg)2.5Al5Si13O36·15(H2O)
Dana No: 77.1.2.4 Strunz No: VIII/J.26-70
Locality:

Notes: