Omphacite Mineral Data

General Omphacite Information

Chemical Formula:

(Ca,Na)(Mg,Fe++,Al)Si2O6

Composition:

Molecular Weight = 211.37 gm

Sodium 3.26 % Na 4.40 % Na₂O

Calcium 11.38 % Ca 15.92 % CaO

Magnesium 6.90 % Mg 11.44 % MgO

Aluminum 3.83 % Al 7.24 % Al₂O₃

Iron 2.64 % Fe 3.40 % FeO

Silicon 26.57 % Si 56.85 % SiO₂

Oxygen 45.42 % O

______ ______

100.00 % 99.24 % = TOTAL OXIDE

Empirical Formula:

Ca_0.6Na_0.3Mg_0.6Al_0.3Fe²⁺_0.1Si₂O₆

Environment:

Major constituent of eclogite, commonly in kimberlite pipes; from some ophiolites and glaucophane-bearing blueschist facies rocks.

IMA Status:

Valid Species (Pre-IMA) 1815

Locality:

Tiburon Pininsula, Marin County, and Sonoma County, California, USA. Link to MinDat.org Location Data.

Name Origin:

From the Greek for "unripe grapes", in allusion to its green color.

Name Pronunciation:

Omphacite + Pronunciation

Synonym:

ICSD 63236

PDF 42-568

Omphacite Image

Images:

Omphacite

Comments: Dark green crystalline omphacite with glaucophane.
Location: Healdsburg, Sonoma County, California, USA. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Omphacite Crystallography

Axial Ratios:

a:b:c =1.0921:1:0.5993

Cell Dimensions:

a = 9.585, b = 8.776, c = 5.26, Z = 4; beta = 106.85° V = 423.46 Den(Calc)= 3.32

Crystal System:

Monoclinic - PrismaticH-M Symbol (2/m) Space Group: P 2/n

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

By Intensity(I/I_o): 2.98(1), 1.4(0.8), 2.13(0.7),

Crystal Structure:

Mouse
drag1 - LMB Manipulate Structure
drag2 - RMB Resize/Rotate
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H - Help Screen
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Clark J R , Papike J J , American Mineralogist , 53 (1968) p.840-868, Crystal-chemical characterization of omphacites

View Additional jPOWD Structure files for Omphacite
[1] [2] [3] [4] [5] [6] [7]

Physical Properties of Omphacite

Cleavage:

{110} Good, {110} Good

Color:

Grass green, Dark green.

Density:

3.29 - 3.39, Average = 3.34

Diaphaneity:

Translucent

Fracture:

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

Habit:

Anhedral Grains - Granular minerals without the expression of crystal shapes

Habit:

Massive - Granular - Common texture observed in granite and other igneous rock.

Hardness:

5-6 - Between Apatite and Orthoclase

Luster:

Vitreous - Silky

Streak:

greenish white

Optical Properties of Omphacite

Gladstone-Dale:

CI meas= -0.014 (Superior) - where the CI = (1-KPDmeas/KC)
CI calc= -0.021 (Excellent) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2085,KPDmeas= 0.2072,KC= 0.2043
Ncalc = 1.67 - 1.69

Optical Data:

Biaxial (+), a=1.662-1.701, b=1.67-1.712, g=1.685-1.723, bire=0.0220-0.0230, 2V(Calc)=74-88, 2V(Meas)=58-83. Dispersion r > v moderate.

Pleochroism (x):

colorless.

Pleochroism (y):

very pale green.

Pleochroism (z):

very pale greenish blue or very pale green.

Calculated Properties of Omphacite

Electron Density:

Bulk Density (Electron Density)=3.32 gm/cc
note: Specific Gravity of Omphacite =3.34 gm/cc.

Fermion Index:

Fermion Index = 0.02
Boson Index = 0.98

Photoelectric:

PE_Omphacite= 3.51 barns/electron
U=PE_Omphacite x rElectron Density= 11.66 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)
Omphacite is Not Radioactive

Omphacite Classification

Dana Class:

65.01.03b.01 (65)Inosilicate Single-Width Unbranched Chains, W=1

(65.01)with chains P=2

(65.01.03b)C2/c clinopyroxenes (intermediate clinopyroxenes)

65.01.03b.01 Omphacite (Ca,Na)(Mg,Fe,Al)Si2O6 P 2/n 2/m

65.01.03b.02 Aegirine-augite* (Ca,Na)(Mg,Fe,Fe)[Si2O6] C 2/c 2/m

Strunz Class:

09.DA.20 09 - SILICATES (Germanates)

09.D - Inosilicates* Structural terminology according to Liebau (1985)

09.DA -Inosilicates with 2-periodic single chains, Si2O6; pyroxene family

09.DA.20 Aegirine-augite* (Ca,Na)(Mg,Fe,Fe)[Si2O6] C 2/c 2/m

09.DA.20 Omphacite (Ca,Na)(Mg,Fe,Al)Si2O6 P 2/n 2/m

Other Omphacite Information

References:

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

See Also:

Links to other databases for Omphacite :
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 - Mineral and Gemstone Kingdom
12 - Mineralienatlas (Deutsch)
13 - Online Mineral Museum
14 - QUT Mineral Atlas
15 - Ruff.Info
16 - WWW-MINCRYST

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Ask about Omphacite here :
Ask-A-Mineralogist from the Mineralogical Society of America
Mindat.org's Discussion Groups
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Print or Cut-and-Paste your Omphacite Specimen Label here :

Omphacite

(Ca,Na)(Mg,Fe++,Al)Si2O6
Dana No: 65.01.03b.01 Strunz No: 09.DA.20
Locality:

Notes: