Member of the clinopyroxene group of silicate minerals
Omphacite
Picture of pieces of eclogite (type of rock) from the Western Gneiss Region in Norway. The rock contains the minerals omphacite (green), pyrope-garnet (red), quartz (milky), kyanite (blue) and some phengite (golden white).
General
Category
Pyroxene
Formula (repeating unit)
(Ca,Na)(Mg,Fe2+,Al)Si2O6
IMA symbol
Omp[1]
Strunz classification
9.DA.20
Dana classification
65.01.03b.01 (clinopyroxene)
Crystal system
Monoclinic
Crystal class
Prismatic (2/m) (same H-M symbol)
Space group
P2/n or C2/c
Unit cell
a = 9.66, b = 8.81, c = 5.22 [Å]; β = 106.56°; Z = 4
Identification
Color
Green to dark green; colorless to pale green in thin section
Crystal habit
Rarely in rough crystals; anhedral, granular to massive
Twinning
Single and polysynthetic twinning common on {100}
Cleavage
Good on {110}, {110} ^ {110} ≈87°; parting on {100}
Weak; X = colorless; Y = very pale green; Z = very pale green, blue-green
2V angle
Measured: 58° to 83°, Calculated: 74° to 88°
References
[2][3][4][5]
Omphacite is a member of the clinopyroxene group of silicate minerals with formula: (Ca, Na)(Mg, Fe2+, Al)Si2O6. It is a variably deep to pale green or nearly colorless variety of clinopyroxene. It normally appears in eclogite, which is the high-pressure metamorphic rock of basalt. Omphacite is the solid solution of Fe-bearing diopside and jadeite.[6] It crystallizes in the monoclinic system with prismatic, typically twinned forms, though usually anhedral. Its space group can be P2/n or C2/c depending on the thermal history.[7] It exhibits the typical near 90° pyroxene cleavage. It is brittle with specific gravity of 3.29 to 3.39 and a Mohs hardness of 5 to 6.
^Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., pp. 398 - 405, John Wiley and Sons, New York ISBN 0-471-80580-7
^Handbook of Mineralogy
^Mindat.org
^Webmineral data
^Hao, Ming; Pierotti, Caroline E.; Tkachev, Sergey; Prakapenka, Vitali; Zhang, Jin S. (2019). "The single-crystal elastic properties of the jadeite-diopside solid solution and their implications for the composition-dependent seismic properties of eclogite". American Mineralogist. 104 (7): 1016–1021. Bibcode:2019AmMin.104.1016H. doi:10.2138/am-2019-6990. ISSN 0003-004X. S2CID 195790171.
^Fleet, M. E.; Herzberg, C. T.; Bancroft, G. M.; Aldridge, L. P. (1978). "Omphacite studies; I, The P2/n-->C2/c transformation". American Mineralogist. 63: 1100–1106.
Omphacite is a member of the clinopyroxene group of silicate minerals with formula: (Ca, Na)(Mg, Fe2+, Al)Si2O6. It is a variably deep to pale green or...
garnet (almandine-pyrope) hosted in a matrix of sodium-rich pyroxene (omphacite). Accessory minerals include kyanite, rutile, quartz, lawsonite, coesite...
than 20 mol.% calcium, magnesium or iron(II) components are known as omphacite and aegirine-augite. With 80% or more of these components the pyroxene...
and/or orthopyroxene. There is also a miscibility gap between augite and omphacite, but this gap occurs at higher temperatures. There are no industrial or...
aluminium. Omphacite is intermediate in composition between jadeite and diopside. However, there is not a true solid solution series, as omphacite has its...
Belgium (flint) Plancher-les-Mines, France (pelite) Aosta Valley, Italy (omphacite). metal axes are still produced and in use today in parts of Papua, Indonesia...
chromian pyrope, chromian spinel, ilmenite, perovskite, zircon, diamond, omphacite, rutile, carbonates and micas. It has been reported from the Red Ledge...
diopside, serpentine, tremolite, forsterite, clinochlore, phlogopite, omphacite and talc. The colour is determined by the coloured mineral content, with...
Eclogite, a rock similar to basalt in composition, is composed primarily of omphacite (sodic clinopyroxene) and pyrope-rich garnet. Eclogite is associated with...
Takashi Yoshino, and Zhenmin Jin: "Measurement of thermal conductivity of omphacite, jadeite, and diopside up to 14 GPa and 1000 K: Implication for the role...
they are not eclogites, as clinopyroxene in them is less sodic than omphacite and the pyroxenite compositions typically are unlike that of basalt. Pyroxenites...
subducted slabs. It is mainly composed of garnet and clinopyroxene (mainly omphacite) up to ~500 km depth (Fig. 4). (3) Harzburgite, it mainly exists under...
other similar-looking, relatively hard greenstones such as albitite, omphacite, chrysoprase, and quartzite. Variation in color is largely due to variation...
delvauxite, hisingerite (amorphous/ poorly cristalline); actinolite, augite, omphacite, sanidine (intermediate member of a solid solution series) are IMA/CNMNC...
geologic record. A common assemblage in lawsonite eclogite is garnet + omphacite + lawsonite + phengite + rutile ± glaucophane. Lawsonite occurs as inclusions...
1017/S0954102099000280 Kim, D., Kim, T., Lee, J. et al., Microfabrics of omphacite and garnet in eclogite from the Lanterman Range, northern Victoria Land...
terrane itself consists of blueschist and eclogite in albite–epidote–omphacite, as well as ferroglaucophane–lawsonite mineral zones. Such mineral assemblages...
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