Omphacite
A valid IMA mineral species
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About Omphacite
Green unripe grapes
Formula:
(NaaCabFe2+cMgd)(AleFe3+fFe2+gMgh)Si2O6
a+b+c+d = 1
e+f+g=h = 1
a = e+f
0.2 ≤ a ≤ 0.8
e > f
e+f+g=h = 1
a = e+f
0.2 ≤ a ≤ 0.8
e > f
Colour:
dark green
Hardness:
5 - 6
Crystal System:
Monoclinic
Member of:
Name:
From the Greek for unripe grape, in allusion to its green colour.
A clinopyroxene intermediate between jadeite and augite, with solid solution towards aegirine-augite. There is a solvus between omphacite (P2/n) and jadeite (C2/c) and also between omphacite and augite/diopside (C2/c), below about 500C. Above this temperature there may be complete solid solution with a disordered C2/c structure. Note the classification diagram of Morimoto doesn’t quite fit the structural changes: some minerals with the jadeite C2/c structure plot in Morimoto’s omphacite field, which should be P2/n below about 500C.
The Ca analogue of UM2001-19-SiO:AlCaMgNa -possibly the Na-dominant “omphacite” with the C2/c structure?
A primary constituent of the high pressure and temperature rock eclogite.
May contain trace water in form of structurally-bound hydroxyl groups. As an example, omphacite from Pohorje Mts., Slovenia, has 530 to 870 ppm H2O (Skogby et al., 2016).
Visit gemdat.org for gemological information about Omphacite.
The Ca analogue of UM2001-19-SiO:AlCaMgNa -possibly the Na-dominant “omphacite” with the C2/c structure?
A primary constituent of the high pressure and temperature rock eclogite.
May contain trace water in form of structurally-bound hydroxyl groups. As an example, omphacite from Pohorje Mts., Slovenia, has 530 to 870 ppm H2O (Skogby et al., 2016).
Visit gemdat.org for gemological information about Omphacite.Unique Identifiers
Mindat ID:
2991
Long-form identifier:
mindat:1:1:2991:5
GUID
(UUID V4):
(UUID V4):
6f722597-f2c9-4bae-83e5-f09a128d2771
Classification of Omphacite
Accepted names for Na pyroxenes. (after Morimoto et al, 1988)
IMA Classification of Omphacite
Approved
IMA Formula:
(Ca,Na)(Mg,Fe,Al)Si2O6
9.DA.20
9 : SILICATES (Germanates)
D : Inosilicates
A : Inosilicates with 2-periodic single chains, Si2O6; pyroxene family
9 : SILICATES (Germanates)
D : Inosilicates
A : Inosilicates with 2-periodic single chains, Si2O6; pyroxene family
65.1.3b.1
65 : INOSILICATES Single-Width,Unbranched Chains,(W=1)
1 : Single-Width Unbranched Chains, W=1 with chains P=2
65 : INOSILICATES Single-Width,Unbranched Chains,(W=1)
1 : Single-Width Unbranched Chains, W=1 with chains P=2
16.24.2
16 : Silicates Containing Aluminum and other Metals
24 : Aluminosilicates of Fe, Mg, Ca and alkalis
16 : Silicates Containing Aluminum and other Metals
24 : Aluminosilicates of Fe, Mg, Ca and alkalis
Mineral Symbols
As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.
Please only use the official IMA–CNMNC symbol. Older variants are listed for historical use only.
Please only use the official IMA–CNMNC symbol. Older variants are listed for historical use only.
| Symbol | Source | Reference |
|---|---|---|
| Omp | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
| Omp | Kretz (1983) | Kretz, R. (1983) Symbols of rock-forming minerals. American Mineralogist, 68, 277–279. |
| Omp | Siivolam & Schmid (2007) | Siivolam, J. and Schmid, R. (2007) Recommendations by the IUGS Subcommission on the Systematics of Metamorphic Rocks: List of mineral abbreviations. Web-version 01.02.07. IUGS Commission on the Systematics in Petrology. download |
| Omp | Whitney & Evans (2010) | Whitney, D.L. and Evans, B.W. (2010) Abbreviations for names of rock-forming minerals. American Mineralogist, 95, 185–187 doi:10.2138/am.2010.3371 |
| Omp | The Canadian Mineralogist (2019) | The Canadian Mineralogist (2019) The Canadian Mineralogist list of symbols for rock- and ore-forming minerals (December 30, 2019). download |
Physical Properties of Omphacite
Optical Data of Omphacite
Type:
Biaxial (+)
RI values:
nα = 1.662 - 1.701 nβ = 1.670 - 1.712 nγ = 1.685 - 1.723
2V:
Measured: 58° to 83°, Calculated: 74° to 88°
Max Birefringence:
δ = 0.023
Image shows birefringence interference colour range (at 30µm thickness)
and does not take into account mineral colouration.
and does not take into account mineral colouration.
Surface Relief:
High
Dispersion:
r > v moderate
Chemistry of Omphacite
Mindat Formula:
(NaaCabFe2+cMgd)(AleFe3+fFe2+gMgh)Si2O6
a+b+c+d = 1
e+f+g=h = 1
a = e+f
0.2 ≤ a ≤ 0.8
e > f
a+b+c+d = 1
e+f+g=h = 1
a = e+f
0.2 ≤ a ≤ 0.8
e > f
Common Impurities:
Ti,Cr,Mn,K,H2O
Chemical Analysis
Oxide wt%:
| 1 | |
|---|---|
| SiO2 | 56.63 % |
| TiO2 | 0.09 % |
| Al2O3 | 14.94 % |
| FeO | 7.22 % |
| MnO | 0 % |
| MgO | 3.45 % |
| CaO | 6.26 % |
| Na2O | 11.05 % |
| K2O | 0 % |
| Total: | 99.64 % |
Sample references:
| ID | Locality | Reference | Notes |
|---|---|---|---|
| 1 | Yingshan, Yingshan Co., Huanggang, Hubei, China | The sample mainly comprise eclogite with garnet and omphacite. Other main constituent minerals are amphibole, epidote, quartz, phengite, kyanite, and rutile. Fine–grained(<1-3µm) symplectite of clinopyroxene+plagioclase partially replaces omphacite Quantitative analyses of major elements were performed using wavelength–dispersive X–ray spectrometry at Okayama University(JEOLJXA–8230). A 15–kV accelerating potential and a 20–nA beam current were employed in the analyses. |
Crystallography of Omphacite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Cell Parameters:
a = 9.66 Å, b = 8.81 Å, c = 5.22 Å
β = 106.56°
β = 106.56°
Ratio:
a:b:c = 1.096 : 1 : 0.593
Unit Cell V:
425.82 ų (Calculated from Unit Cell)
Comment:
Space group may be C2/c or P2/n.
Crystal Structure
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Data courtesy of the American Mineralogist Crystal Structure Database. Click on an AMCSD ID to view structure
| ID | Species | Reference | Link | Year | Locality | Pressure (GPa) | Temp (K) |
|---|---|---|---|---|---|---|---|
| 0000175 | Omphacite | Clark J R, Papike J J (1968) Crystal-chemical characterization of omphacites American Mineralogist 53 840-868 |  | 1968 | 0 | 293 | |
| 0000466 | Omphacite | Matsumoto T, Tokonami M, Morimoto N (1975) The crystal structure of omphacite American Mineralogist 60 634-641 | | 1975 | 0 | 293 | |
| 0001054 | Omphacite | McCormick T C (1986) Crystal-chemical aspects of nonstoichiometric pyroxenes American Mineralogist 71 1434-1440 | | 1986 | 0 | 293 | |
| 0001055 | Omphacite | McCormick T C (1986) Crystal-chemical aspects of nonstoichiometric pyroxenes American Mineralogist 71 1434-1440 | | 1986 | 0 | 293 | |
| 0001056 | Omphacite | McCormick T C (1986) Crystal-chemical aspects of nonstoichiometric pyroxenes American Mineralogist 71 1434-1440 | | 1986 | 0 | 293 | |
| 0005103 | Omphacite | Curtis L, Gittins J, Kocman V, Rucklidge J C, Hawthorne F C, Ferguson R B (1975) Two crystal structure refinements of a P2/n titanian ferro-omphacite The Canadian Mineralogist 13 62-67 | | 1975 | 0 | 293 | |
| 0005104 | Omphacite | Curtis L, Gittins J, Kocman V, Rucklidge J C, Hawthorne F C, Ferguson R B (1975) Two crystal structure refinements of a P2/n titanian ferro-omphacite The Canadian Mineralogist 13 62-67 | | 1975 | 0 | 293 | |
| 0014547 | Omphacite | Pavese A, Bocchio R, Ivaldi G (2000) In situ high temperature single crystal X-ray diffraction study of a natural omphacite Mineralogical Magazine 64 983-993 | | 2000 | Gorduno, Lepontine Alps, Switzerland | 0 | 293 |
| 0014548 | Omphacite | Pavese A, Bocchio R, Ivaldi G (2000) In situ high temperature single crystal X-ray diffraction study of a natural omphacite Mineralogical Magazine 64 983-993 | | 2000 | Gorduno, Lepontine Alps, Switzerland | 0 | 293 |
| 0014549 | Omphacite | Pavese A, Bocchio R, Ivaldi G (2000) In situ high temperature single crystal X-ray diffraction study of a natural omphacite Mineralogical Magazine 64 983-993 | | 2000 | Gorduno, Lepontine Alps, Switzerland | 0 | 293 |
| 0015676 | Omphacite | Mottana A, Rossi G, Kracher A, Kurat G (1979) Violan revisited: Mn-bearing omphacite and diopside Tschermaks Mineralogische und Petrographische Mitteilungen 26 187-201 | 1979 | manganese deposit of Praborna, St Marcel, Aosta Valley, Italy | 0 | 293 |
CIF Raw Data - click here to close
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 3a: Earth’s earliest Hadean crust | >4.50 |
| 7 : Ultramafic igneous rocks | |
| Stage 3b: Earth’s earliest hydrosphere | >4.45 |
| 12 : Hadean hydrothermal subsurface sulfide deposits (see also #33) | |
| Stage 4b: Highly evolved igneous rocks | >3.0 |
| 36 : Carbonatites, kimberlites, and related igneous rocks | |
| Stage 5: Initiation of plate tectonics | <3.5-2.5 |
| 39 : High-𝑃 metamorphism (blueschist, eclogite, ultrahigh 𝑃 facies) | |
| 40 : Regional metamorphism (greenschist, amphibolite, granulite facies) |
Type Occurrence of Omphacite
Synonyms of Omphacite
Other Language Names for Omphacite
Varieties of Omphacite
| Chrome-Omphacite | A chrome-rich variety of Omphacite |
| Titanium-bearing Omphacite | An omphacite with at least 0.10 Ti4+ cations in the M1 position in the clinopyroxene structure. Additional Na+ cations replacing divalent cations in the M2 position are needed to obtain charge balance. |
Relationship of Omphacite to other Species
Member of:
Other Members of this group:
| Aegirine | NaFe3+Si2O6 | Mon. 2/m : B2/b |
| Aegirine-augite | (NaaCabFe2+cMgd)(Fe3+eAlfFe2+gMgh)Si2O6 | Mon. 2/m : B2/b |
| Augite | (CaxMgyFez)(Mgy1Fez1)Si2O6 | Mon. 2/m : B2/b |
| Burnettite | CaVAlSiO6 | Mon. 2/m : B2/b |
| Clinoenstatite | MgSiO3 | Mon. 2/m : P21/b |
| Clinoferrosilite | Fe2+2Si2O6 | Mon. 2/m : P21/b |
| Colomeraite | NaTi3+Si2O6 | Mon. 2/m : B2/b |
| Davisite | CaScAlSiO6 | Mon. 2/m : B2/b |
| Diopside | CaMgSi2O6 | Mon. 2/m : B2/b |
| Esseneite | CaFe3+[AlSiO6] | Mon. 2/m : B2/b |
| Grossmanite | CaTi3+ AlSiO6 | Mon. 2/m : B2/b |
| Hedenbergite | CaFe2+Si2O6 | Mon. 2/m : B2/b |
| Jadeite | Na(Al,Fe3+)Si2O6 | Mon. 2/m : B2/b |
| Jervisite | NaSc3+Si2O6 | Mon. 2/m : B2/b |
| Johannsenite | CaMn2+Si2O6 | Mon. 2/m : B2/b |
| Kanoite | Mn2+(Mg,Mn2+)Si2O6 | Mon. 2/m : P21/b |
| Kosmochlor | NaCrSi2O6 | Mon. 2/m : B2/b |
| Kushiroite | CaAl[AlSiO6] | Mon. 2/m : B2/b |
| Namansilite | NaMn3+Si2O6 | Mon. 2/m : B2/b |
| Natalyite | NaV3+Si2O6 | Mon. 2/m : B2/b |
| Petedunnite | Ca(Zn,Mn2+,Mg,Fe2+)Si2O6 | Mon. 2/m : B2/b |
| Pigeonite | (CaxMgyFez)(Mgy1Fez1)Si2O6 | Mon. 2/m : P21/b |
| Ryabchikovite | CuMgSi2O6 | Mon. 2/m : P21/b |
| Spodumene | LiAlSi2O6 | Mon. 2/m : B2/b |
| Tissintite | (Ca,Na,◻)AlSi2O6 | Mon. 2/m : B2/b |
| UM2001-19-SiO:AlCaMgNa | (Na,Mg,Ca)(Mg,Al)Si2O6 | Mon. 2/m : B2/b |
| UM2003-36-SiO:CaNa | NaCrSi2O6 - CaMgSi2O6 | Mon. 2/m : B2/b |
Common Associates
Associated Minerals Based on Photo Data:
| 23 photos of Omphacite associated with Garnet Group | X3Z2(SiO4)3 |
| 10 photos of Omphacite associated with Glaucophane | ◻[Na2][Mg3Al2]Si8O22(OH)2 |
| 9 photos of Omphacite associated with Kyanite | Al2(SiO4)O |
| 7 photos of Omphacite associated with Almandine | Fe2+3Al2(SiO4)3 |
| 6 photos of Omphacite associated with Pyrope | Mg3Al2(SiO4)3 |
| 5 photos of Omphacite associated with Ruby | Al2O3 |
| 4 photos of Omphacite associated with Titanite | CaTi(SiO4)O |
| 3 photos of Omphacite associated with Eclogite | |
| 3 photos of Omphacite associated with Barroisite | ◻{CaNa}{Mg3Al2}(AlSi7O22)(OH)2 |
| 3 photos of Omphacite associated with Almandine-Pyrope Series |
Related Minerals - Strunz-mindat Grouping
| 9.DA. | Protoenstatite | Mg2Si2O6 |
| 9.DA. | Ryabchikovite | CuMgSi2O6 |
| 9.DA. | Colomeraite | NaTi3+Si2O6 |
| 9.DA.05 | Donpeacorite | (Mn,Mg)MgSi2O6 |
| 9.DA.05 | Enstatite | Mg2Si2O6 |
| 9.DA.05 | Ferrosilite | Fe2+2Si2O6 |
| 9.DA.10 | Clinoenstatite | MgSiO3 |
| 9.DA.10 | Clinoferrosilite | Fe2+2Si2O6 |
| 9.DA.10 | Kanoite | Mn2+(Mg,Mn2+)Si2O6 |
| 9.DA.10 | Pigeonite | (CaxMgyFez)(Mgy1Fez1)Si2O6 |
| 9.DA.15 | Augite | (CaxMgyFez)(Mgy1Fez1)Si2O6 |
| 9.DA.15 | Diopside | CaMgSi2O6 |
| 9.DA.15 | Esseneite | CaFe3+[AlSiO6] |
| 9.DA.15 | Hedenbergite | CaFe2+Si2O6 |
| 9.DA.15 va | Jeffersonite | Ca(Mn,Zn,Fe)Si2O6 |
| 9.DA.15 | Johannsenite | CaMn2+Si2O6 |
| 9.DA.15 | Petedunnite | Ca(Zn,Mn2+,Mg,Fe2+)Si2O6 |
| 9.DA.15 | Davisite | CaScAlSiO6 |
| 9.DA.15 | Kushiroite | CaAl[AlSiO6] |
| 9.DA.15 | Grossmanite | CaTi3+ AlSiO6 |
| 9.DA.20 | Aegirine-augite | (NaaCabFe2+cMgd)(Fe3+eAlfFe2+gMgh)Si2O6 |
| 9.DA.25 | Aegirine | NaFe3+Si2O6 |
| 9.DA.25 | Jadeite | Na(Al,Fe3+)Si2O6 |
| 9.DA.25 | Jervisite | NaSc3+Si2O6 |
| 9.DA.25 | Kosmochlor | NaCrSi2O6 |
| 9.DA.25 | Namansilite | NaMn3+Si2O6 |
| 9.DA.25 | Natalyite | NaV3+Si2O6 |
| 9.DA.25 | Tissintite | (Ca,Na,◻)AlSi2O6 |
| 9.DA.30 | Spodumene | LiAlSi2O6 |
| 9.DA.35 | Hiroseite | FeSiO3 |
Other Information
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.
Omphacite in petrology
An essential component of rock names highlighted in red, an accessory component in rock names highlighted in green.
Internet Links for Omphacite
mindat.org URL:
https://www.mindat.org/min-2991.html
Please feel free to link to this page.
Please feel free to link to this page.
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References for Omphacite
Reference List:
Werner, Abraham Gottlob (1817) Letztes Mineral-System - Aus dessen Nachlasse auf oberbergamtliche Anordnung herausgegeben und mit Erläuterungen versehen.pages 33-34 and 42-43
forum.amiminerals.it (n.d.) http://forum.amiminerals.it/viewtopic.php?f=5&t=17502&sid=0cdf430f875452c51b8085303c78a701
Localities for Omphacite
symbol to view information about a locality.
The Locality List
- This locality has map coordinates listed.
- This locality has estimated coordinates.
ⓘ - Click for references and further information on this occurrence.
? - Indicates mineral may be doubtful at this locality.
- Good crystals or important locality for species.
- World class for species or very significant.
(TL) - Type Locality for a valid mineral species.
(FRL) - First Recorded Locality for everything else (eg varieties).
All localities listed without proper references should be considered as questionable.
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Bric Vert, Quincinetto, Metropolitan City of Turin, Piedmont, Italy