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 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:

Mouse
drag1 - LMB Manipulate Structure
drag2 - RMB Resize/Rotate
Keyboard
S - Stereo Pair on/off
H - Help Screen
I - Data Info
A - Atoms On/Off
P - Polyhedra On/Off
B - Bonds On/Off
Help on Above

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

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 – 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

Search for Offretite using:

[AOL] [Bing] [Dog Pile] [GeoScienceWorld] [HotBot] [Ixquick] [Lycos] [MAMMA] [Scirus] [Teoma] [WebCrawler] [Wikipedia] [YAHOO]

Visit our Advertisers for Offretite :

A Bijoux Google Search for Offretite
Adam's Minerals Google Search for Offretite
Cape Minerals Google Search for Offretite
Dakota Matrix Minerals Google Search for Offretite
Excalibur Mineral Corp. Google Search for Offretite
Exceptional Minerals Google Search for Offretite
John Betts Fine Minerals Search for Offretite
McDougall Minerals Google Search for Offretite
Mineral News Website Link
Rock and Mineral Shows Google Search for Offretite
Weinrich Minerals, Inc. Google Search for Offretite

Ask about Offretite here :
Ask-A-Mineralogist from the Mineralogical Society of America
Mindat.org's Discussion Groups
Original Rockhounds Discussion Group
Rockhounds Discussion Group on Yahoo Groups
Mineral Discussion Forum from Fabre Minerals - also available in Español

Print or Cut-and-Paste your Offretite Specimen Label here :

Offretite

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

Notes: