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Omphacite
| Omphacite | |
|---|---|
 | |
| 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} |
| Fracture | Uneven to conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 5–6 |
| Luster | Vitreous to silky |
| Streak | Greenish white |
| Diaphaneity | Translucent |
| Specific gravity | 3.16–3.43 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.662 – 1.701 nβ = 1.670 – 1.712 nγ = 1.685 – 1.723 |
| Birefringence | δ = 0.023 |
| Pleochroism | 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.
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ 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.
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