Omphacite Mineral Data

Omphacite Mineral Data +

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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.

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:

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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

Diaphaniety:

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

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:

r_electron=3.32 gm/cc
note: r_Omphacite=3.34 gm/cc.

Fermion Index

Fermion Index = 0.02024
Boson Index = 0.97976

Photoelectric:

PE_Omphacite= 3.51 barns/electron
U=PE_Omphacite x r_electron= 11.66 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Omphacite is Not Radioactive

Omphacite Classification

Dana Class:

65.1.3b.1 (65)Inosilicate Single-Width Unbranched Chains, W=1

(65.1)with chains P=2

(65.1.3b)C2/c clinopyroxenes (intermediate clinopyroxenes)

65.1.3b.1 Omphacite (Ca,Na)(Mg,Fe,Al)Si2O6 P 2/n 2/m

65.1.3b.2 Aegirine-augite* (Ca,Na)(Mg,Fe,Fe)[Si2O6] C 2/c 2/m

Strunz Class:

VIII/F.01-100 VIII - Silicates

VIII/F - Inosilicates (chain and band) double chains [Si2O6]4-

VIII/F.01 - Pyroxene group, Clinopyroxene

VIII/F.01-10 Clinoenstatite Mg2Si2O6 P 2₁/c 2/m

VIII/F.01-20 Clinoferrosilite (Fe,Mg)2Si2O6 P 2₁/c 2/m

VIII/F.01-30 Kanoite (Mn,Mg)2Si2O6 P 2₁/c 2/m

VIII/F.01-40 Pigeonite (Mg,Fe,Ca)(Mg,Fe)Si2O6 P 2₁/c 2/m

VIII/F.01-50 Diopside CaMgSi2O6 C 2/c 2/m

VIII/F.01-60 Hedenbergite CaFeSi2O6 C 2/c 2/m

VIII/F.01-70 Johannsenite CaMnSi2O6 C 2/c 2/m

VIII/F.01-80 Petedunnite Ca(Zn,Mn,Fe,Mg)Si2O6 C 2/c 2/m

VIII/F.01-90 Augite (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6 C 2/c 2/m

VIII/F.01-100 Omphacite (Ca,Na)(Mg,Fe,Al)Si2O6 P 2/n 2/m

VIII/F.01-110 Esseneite CaFeAlSiO6 C 2/c 2/m

VIII/F.01-120 Spodumene LiAlSi2O6 C 2/c 2/m

VIII/F.01-130 Jadeite Na(Al,Fe)Si2O6 C 2/c 2/m

VIII/F.01-140 Aegirine NaFeSi2O6 C 2/c 2/m

VIII/F.01-145 Namansilite NaMn(Si2O6) C 2/c 2/m

VIII/F.01-150 Jervisite (Na,Ca,Fe)(Sc,Mg,Fe)Si2O6 C 2/c 2/m

VIII/F.01-160 Natalyite Na(V,Cr)Si2O6 C 2/c 2/m

VIII/F.01-170 Kosmochlor NaCrSi2O6 C 2/c 2/m

Other Omphacite Information

References:

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

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Omphacite

(Ca,Na)(Mg,Fe++,Al)Si2O6
Dana No: 65.1.3b.1 Strunz No: VIII/F.01-100
Locality:

Notes: