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Omphacite

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Formula:
(Ca,Na)(Mg,Al)Si
 
2
O
 
6
System:MonoclinicColour:dark green
Hardness:5 - 6
Member of:Clinopyroxene Subgroup > Pyroxene Group
Name:From the Greek for unripe grape, in allusion to its green colour.


Pyroxene Group.
A clinopyroxene solid solution of jadeite (25%-75%), augite (25%-75%), and aegirine (0%-25%).
Retained as a distinct species for practical reasons.

A primary constituent of the rock eclogite.

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Classification of Omphacite

IMA status:Approved
Strunz 8th edition ID:8/F.01-100
Nickel-Strunz 10th (pending) edition ID:9.DA.20

9 : SILICATES (Germanates)
D : Inosilicates
A : Inosilicates with 2-periodic single chains, Si2O6; pyroxene family
Dana 8th edition ID:65.1.3b.1

65 : INOSILICATES Single-Width,Unbranched Chains,(W=1)
1 : Single-Width Unbranched Chains, W=1 with chains P=2
Hey's CIM Ref.:16.24.2

16 : Silicates Containing Aluminum and other Metals
24 : Aluminosilicates of Fe, Mg, Ca and alkalis
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Type Occurrence of Omphacite

Type Locality:Eclogite outcrops, Weißenstein, Stammbach, Münchberg Metamorphic complex, Franconia, Bavaria, Germany
Year of Discovery:1815

Physical Properties of Omphacite

Colour:dark green
Streak:greenish white
Hardness (Mohs):5 - 6
Cleavage:Distinct/Good

Crystallography of Omphacite

Crystal System:Monoclinic
Class (H-M):2/m - Prismatic
Cell Parameters:a = 9.66Å, b = 8.81Å, c = 5.22Å
β = 106.56°
Ratio:a:b:c = 1.096 : 1 : 0.593
Unit Cell Volume:V 425.82 ų (Calculated from Unit Cell)
Comment:Space group may be C2/c or P2/n.

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°
Maximum Birefringence:δ = 0.023

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:High
Dispersion:r > v moderate

Chemical Properties of Omphacite

Formula:
(Ca,Na)(Mg,Al)Si
 
2
O
 
6
Simplified for copy/paste:(Ca,Na)(Mg,Al)Si2O6
Essential elements:Ca, Mg, O, Si
All elements listed in formula:Al, Ca, Mg, Na, O, Si
Common Impurities:Ti,Cr,Mn,K,H2O

Relationship of Omphacite to other Species

Member of:Clinopyroxene Subgroup > Pyroxene Group
Other Members of Group:

- +
Aegirine
NaFe
3+
 
Si
 
2
O
 
6
Aegirine-augite
(Na,Ca)(Fe
3+
 
,Fe
2+
 
,Mg,Al)Si
 
2
O
 
6
Augite
(Ca,Na)(Mg,Fe
2+
 
,Al,Fe
3+
 
,Ti)[(Si,Al)
 
2
O
 
6
]
Clinoenstatite
MgSiO
 
3
Clinoferrosilite
Fe
2+
 
SiO
 
3
Diopside
CaMgSi
 
2
O
 
6
Esseneite
CaFe
3+
 
[AlSiO
 
6
]
Grossmanite
CaTi
3+
 
AlSiO
 
6
Hedenbergite
CaFe
2+
 
Si
 
2
O
 
6
Jadeite
Na(Al,Fe
3+
 
)Si
 
2
O
 
6
Jervisite
(Na,Ca,Fe
2+
 
)(Sc,Mg,Fe
2+
 
)Si
 
2
O
 
6
Johannsenite
CaMn
2+
 
Si
 
2
O
 
6
Kanoite
Mn
2+
 
(Mg,Mn
2+
 
)Si
 
2
O
 
6
Kosmochlor
NaCrSi
 
2
O
 
6
Kushiroite
CaAl[AlSiO
 
6
]
Namansilite
NaMn
3+
 
Si
 
2
O
 
6
Natalyite
Na(V
3+
 
,Cr)Si
 
2
O
 
6
Petedunnite
Ca(Zn,Mn
2+
 
,Mg,Fe
2+
 
)Si
 
2
O
 
6
Pigeonite
(Mg,Fe
2+
 
,Ca)(Mg,Fe
2+
 
)Si
 
2
O
 
6
Spodumene
LiAlSi
 
2
O
 
6
Related Minerals - Nickel-Strunz Grouping):

- +
9.DA.05Donpeacorite
(Mn
2+
 
,Mg)Mg[SiO
 
3
]
 
2
9.DA.05Enstatite
MgSiO
 
3
9.DA.05Ferrosilite
FeSiO
 
3
9.DA.10Clinoenstatite
MgSiO
 
3
9.DA.10Clinoferrosilite
Fe
2+
 
SiO
 
3
9.DA.10Kanoite
Mn
2+
 
(Mg,Mn
2+
 
)Si
 
2
O
 
6
9.DA.10Pigeonite
(Mg,Fe
2+
 
,Ca)(Mg,Fe
2+
 
)Si
 
2
O
 
6
9.DA.15Augite
(Ca,Na)(Mg,Fe
2+
 
,Al,Fe
3+
 
,Ti)[(Si,Al)
 
2
O
 
6
]
9.DA.15Diopside
CaMgSi
 
2
O
 
6
9.DA.15Esseneite
CaFe
3+
 
[AlSiO
 
6
]
9.DA.15Hedenbergite
CaFe
2+
 
Si
 
2
O
 
6
9.DA.15Johannsenite
CaMn
2+
 
Si
 
2
O
 
6
9.DA.15Petedunnite
Ca(Zn,Mn
2+
 
,Mg,Fe
2+
 
)Si
 
2
O
 
6
9.DA.15Davisite
CaScAlSiO
 
6
9.DA.15Kushiroite
CaAl[AlSiO
 
6
]
9.DA.15Grossmanite
CaTi
3+
 
AlSiO
 
6
9.DA.20Aegirine-augite
(Na,Ca)(Fe
3+
 
,Fe
2+
 
,Mg,Al)Si
 
2
O
 
6
9.DA.25Aegirine
NaFe
3+
 
Si
 
2
O
 
6
9.DA.25Jadeite
Na(Al,Fe
3+
 
)Si
 
2
O
 
6
9.DA.25Jervisite
(Na,Ca,Fe
2+
 
)(Sc,Mg,Fe
2+
 
)Si
 
2
O
 
6
9.DA.25Kosmochlor
NaCrSi
 
2
O
 
6
9.DA.25Namansilite
NaMn
3+
 
Si
 
2
O
 
6
9.DA.25Natalyite
Na(V
3+
 
,Cr)Si
 
2
O
 
6
9.DA.30Spodumene
LiAlSi
 
2
O
 
6
Related Minerals - Hey's Index Grouping:

- +
16.24.1Aegirine-augite
(Na,Ca)(Fe
3+
 
,Fe
2+
 
,Mg,Al)Si
 
2
O
 
6
16.24.4Ferri-katophorite
Na(CaNa)(Mg
 
4
Fe
3+
 
)(AlSi
 
7
O
 
22
)(OH)
 
2
16.24.5Ferro-ferri-katophorite
NaCaNaFe
2+
4
(Fe
3+
 
)[(AlSi
 
7
)O
 
22
](OH)
 
2
16.24.6Barroisite
☐{CaNa}{Mg
 
3
Al
 
2
}(AlSi
 
7
O
 
22
)(OH)
 
2
16.24.7Ferri-barroisite
☐(CaNa)(Mg
 
3
Fe
3+
2
)(AlSi
 
7
O
 
22
)(OH)
 
2
16.24.8Alumino-ferrobarroisite
☐{CaNa}{Fe
2+
3
Al
 
2
}(AlSi
 
7
O
 
22
)(OH)
 
2
16.24.9Ferro-barroisite
☐{CaNa}{Fe
2+
3
Al
 
2
}(AlSi
 
7
O
 
22
)(OH)
 
2
16.24.10Ferro-ferri-barroisite
☐(CaNa)(Fe
2+
3
Fe
3+
2
)(AlSi
 
7
O
 
22
)(OH)
 
2
16.24.11Hastingsite
{Na}{Ca
 
2
}{Fe
2+
4
Fe
3+
 
}(Al
 
2
Si
 
6
O
 
22
)(OH)
 
2
16.24.12Magnesio-hastingsite
{Na}{Ca
 
2
}{Mg
 
4
Fe
3+
 
}(Al
 
2
Si
 
6
O
 
22
)(OH)
 
2
16.24.13Taramite Root Name
A(CaNa)(Z
2+
3
Z
3+
2
)(Al
 
2
Si
 
6
O
 
22
)(OH,F,Cl)
 
2
16.24.14Ferri-taramite
Na(CaNa)(Mg
 
3
Fe
3+
2
)(Al
 
2
Si
 
6
O
 
22
)(OH)
 
2
16.24.15Magnesiotaramite
{Na}{CaNa}{Mg
 
3
AlFe
3+
 
}(Al
 
2
Si
 
6
O
 
22
)(OH)
 
2
16.24.16Osumilite-(Mg)
KMg
 
2
Al
 
3
(Al
 
2
Si
 
10
)O
 
30
16.24.16Osumilite
(K,Na)(Fe
2+
 
,Mg)
 
2
(Al,Fe
3+
 
)
 
3
(Si,Al)
 
12
O
 
30

Other Names for Omphacite

Synonyms:
DiopsidjadeiteJadeite-DiopsideMayaiteTuxtlite
Other Languages:
Dutch:Omfaciet
French:Omphacite
German:Diopsidjadeit
Mayait
Mexikanischer Jadeit
Omphacit
Omphazit
Tuxtlit
Japanese:オンファス輝石
Polish:Omfacyt
Portuguese:Onfacite
Russian:Омфацит
Simplified Chinese:绿辉石
Spanish:Diopsidjadeita
Mayaita
Omphacita
Tuxtlita
Varieties:
Chrome-OmphaciteOmphacite JadeTitanian Omphacite

Other Information

Health Warning:No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Omphacite

Reference List:

- +
Clark, Joan R. & J.J. Papike (1968), Crystal chemistry characterization of omphacites: American Mineralogist: 53: 840-868.

Clark, Joan R. & J.J. Papike (1969), Cation distribution in the crystal structure of omphacite, the eclogitic pyroxene: Geological Society of America Abstract for 1968.

Edgar, A.D., A. Mottana & N.D. MacRae (1969), The chemistry and cell parameters of omphacite and related pyroxenes: Mineralogical Magazine: 37: 61-74.

Champness, P.E. (1973), Speculation on an order-disorder transformation in omphacite: American Mineralogist: 58: 540-542.

Aldridge, L.P., Bancroft, G.M., Fleet, M.E., and Herzberg, C.T. (1978): Omphacite studies. II. Mössbauer spectra of C2/c and P2/n omphacites. American Mineralogist: 63: 1107-1115.

A. Mottana, G. Rossi, A. Kracher, G. Kurat (1979): Violan revisited: Mn-bearing omphacite and diopside. Tschermaks mineralogische und petrographische Mitteilungen 26, 187-201.

European Journal of Mineralogy (1998): 10: 889.

Katerinopoulou, A.; Katerinopoulos, A.; Bieniok, A.; Knop, E.; Magganas, A.; Amthauer, G. (2007): Crystal chemistry, structure analyses and phase transition experiment on an omphacite from eclogitic metagabbro from Syros island, Greece. Mineralogy and Petrology 91, 117-128.

Internet Links for Omphacite

Search Engines:
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  • External Links:
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  • Look for Omphacite on Wikipedia
  • Look for Omphacite on Mineralien Atlas
  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
  • Omphacite details from Handbook of Mineralogy (PDF)
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