General Offretite Information
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Chemical Formula: |
(K2,Ca,Mg)2.5Al5Si13O36·15(H2O) |
Composition: |
Molecular Weight = 1,453.72 gm |
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Potassium 2.96 % K 3.56 % K2O |
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Calcium 3.03 % Ca 4.24 % CaO |
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Magnesium 1.17 % Mg 1.94 % MgO |
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Aluminum 9.65 % Al 18.24 % Al2O3 |
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Silicon 24.73 % Si 52.90 % SiO2 |
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Hydrogen 2.11 % H 18.84 % H2O |
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Oxygen 56.35 % O |
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______ ______ |
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100.00 % 99.72 % = TOTAL OXIDE |
Empirical Formula: |
K1.1Ca1.1Mg0.7Al5.2Si12.8O36·15.2(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 |
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PDF 25-1186 |
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Offretite Image |
Images:
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Offretite Crystallography
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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 |
X Ray Diffraction: |
By Intensity(I/Io): 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
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[2]
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Physical Properties of Offretite
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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 |
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Optical Properties of Offretite
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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. |
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Calculated Properties of Offretite
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Electron Density: |
relectron=2.16 gm/cc note: rOffretite =2.13 gm/cc. |
Fermion Index |
Fermion Index = 0.01303 Boson Index = 0.98697 |
Photoelectric: |
PEOffretite = 1.96 barns/electron U=PEOffretite x relectron= 4.24 barns/cc. |
Radioactivity: |
GRapi = 43.33 (Gamma Ray American Petroleum Institute Units)
Estimated Radioactivity from Offretite - barely detectable
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Offretite Classification
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Dana Class: |
77.1.2.4 (77)Tectosilicate Zeolite group |
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(77.1)true zeolites |
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(77.1.2)Chabazite and related species |
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77.1.2.1 Chabazite-Ca (Ca0.5,Na,K)4[Al4Si8O24]·12H2O P1 1 |
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77.1.2.1a Chabazite-Na! (Na2,K2,Ca,Mg)[Al2Si4O12]·6(H2O) R 3m 3 2/m |
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77.1.2.1b Chabazite-K! (K2,Ca,Na2,Mg)[Al2Si4O12]·6(H2O) R 3m 3 2/m |
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77.1.2.1c Chabazite-Sr! (Sr,Ca,K2,Na2)[Al2Si4O12]·6(H2O) R 3m 3 2/m |
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77.1.2.2 Herschelite? (Na,Ca,K)AlSi2O6·3(H2O) R 3m 3 2/m |
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77.1.2.3 Willhendersonite KCaAl3Si3O12·5(H2O) P1 1 |
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77.1.2.4 Offretite (K2,Ca,Mg)2.5Al5Si13O36·15(H2O) P 6m2 6 m2 |
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77.1.2.5 Erionite-Na (Na2,K2,Ca)2[Al4Si14O36]·15(H2O) P 63/mmc 6/m 2/m 2/m |
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77.1.2.5a Erionite-K! (K2,Ca,Na2)2[Al4Si14O36]·15(H2O) P 63/mmc 6/m 2/m 2/m |
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77.1.2.5b Erionite-Ca! (Ca,K2,Na2)2[Al4Si14O36]·15(H2O) P 63/mmc 6/m 2/m 2/m |
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77.1.2.6 Gmelinite-Na (Na2,Ca)Al2Si4O12·6(H2O) P 63/mmc 6/m 2/m 2/m |
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77.1.2.6a Gmelinite-Ca! (Ca,Na2)Al2Si4O12·6(H2O) P 63/mmc 6/m 2/m 2/m |
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77.1.2.6b Gmelinite-K! (K,Na,Ca)6(Al7Si17O48)·22(H2O) P 63/mmc 6/m 2/m 2/m |
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77.1.2.7 Faujasite-Na (Na2,Ca,Mg)3.5[Al7Si17O48]·32(H2O) F d3m 4/m 3 2/m |
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77.1.2.7a Faujasite-Ca! (Ca,Na2,Mg)3.5[Al7Si17O48]·32(H2O) F d3m 4/m 3 2/m |
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77.1.2.7b Faujasite-Mg! (Mg,Na2,Ca)3.5[Al7Si17O48]·32(H2O) F d3m 4/m 3 2/m |
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77.1.2.8 Levyne-Ca (Ca,Na2,K2)Al2Si4O12·6(H2O) R 3m 3 2/m |
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77.1.2.8a Levyne-Na! (Na2,Ca,K2)Al2Si4O12·6(H2O) R 3m 3 2/m |
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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 |
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VIII/J - Tectosilicates (network), with zeolite-structure, Bladed Zeolites |
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VIII/J.26 - Zeolite group, Willhendersonite - Chabazite - Perialite series |
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VIII/J.26-10 Willhendersonite KCaAl3Si3O12·5(H2O) P1 1 |
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VIII/J.26-20 Chabazite-Na! (Na2,K2,Ca,Mg)[Al2Si4O12]·6(H2O) R 3m 3 2/m |
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VIII/J.26-25 Chabazite-K! (K2,Ca,Na2,Mg)[Al2Si4O12]·6(H2O) R 3m 3 2/m |
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VIII/J.26-30 Chabazite-Ca (Ca0.5,Na,K)4[Al4Si8O24]·12H2O P1 1 |
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VIII/J.26-35 Chabazite-Sr! (Sr,Ca,K2,Na2)[Al2Si4O12]·6(H2O) R 3m 3 2/m |
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VIII/J.26-40 Tschernichite (Ca,Na)(Si6Al2)O16·4-8(H2O) P 4/mmm 4/m 2/m 2/m |
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VIII/J.26-50 Gmelinite-Na (Na2,Ca)Al2Si4O12·6(H2O) P 63/mmc 6/m 2/m 2/m |
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VIII/J.26-52 Gmelinite-K! (K,Na,Ca)6(Al7Si17O48)·22(H2O) P 63/mmc 6/m 2/m 2/m |
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VIII/J.26-54 Gmelinite-Ca! (Ca,Na2)Al2Si4O12·6(H2O) P 63/mmc 6/m 2/m 2/m |
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VIII/J.26-58 Levyne-Na! (Na2,Ca,K2)Al2Si4O12·6(H2O) R 3m 3 2/m |
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VIII/J.26-60 Levyne-Ca (Ca,Na2,K2)Al2Si4O12·6(H2O) R 3m 3 2/m |
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VIII/J.26-70 Offretite (K2,Ca,Mg)2.5Al5Si13O36·15(H2O) P 6m2 6 m2 |
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VIII/J.26-80 Mazzite K2CaMg2(Al,Si)36O72·28(H2O) P 63/mmc 6/m 2/m 2/m |
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VIII/J.26-90 Erionite-Na (Na2,K2,Ca)2[Al4Si14O36]·15(H2O) P 63/mmc 6/m 2/m 2/m |
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VIII/J.26-92 Erionite-K! (K2,Ca,Na2)2[Al4Si14O36]·15(H2O) P 63/mmc 6/m 2/m 2/m |
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VIII/J.26-94 Erionite-Ca! (Ca,K2,Na2)2[Al4Si14O36]·15(H2O) P 63/mmc 6/m 2/m 2/m |
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VIII/J.26-95 Bellbergite (K,Ba,Sr)2Sr2Ca2(Ca,Na)4Al18Si18O72·30(H2O) P 63/mmc, P 62c-, P 63mc Hex |
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VIII/J.26-100 Perlialite K8Tl4Al12Si24O72·20(H2O) P 6/mmm 6/m 2/m 2/m |
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Other Offretite Information
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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 - Crocoite.com Mineral Locations
4 - EUROmin Project
5 -Google Images
6 -Google Scholar
7 -Handbook of Mineralogy (MinSocAm)
8 -Handbook of Mineralogy (UofA)
9 -MinDAT
10 -MinMax(Deutsch)
11 -MinMax(English)
12 -Mineralienatlas (Deutsch)
13 -QUT Mineral Atlas
14 - WWW-MINCRYST
15 -Zeolite Database by Bruno Herreros
16 -École des Mines de Paris
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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:
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