Ephesite | |
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General | |
Category | Phyllosilicate |
Formula (repeating unit) | NaLiAl2(Al2Si2)O10(OH)2 |
IMA symbol | Eph[1] |
Strunz classification | 9.EC.20 |
Crystal system | Monoclinic |
Crystal class | Prismatic (2/m) (same H-M symbol) |
Space group | C2/c[2] also reported is a triclinic polytype[3] |
Unit cell | a = 5.12, b = 8.853 c = 19.303 [Å]; beta = 95.08°; Z = 4 |
Identification | |
Color | Brownish pink, pearl gray, pale green |
Crystal habit | Flakes |
Twinning | Commonly twinned about [310] or [310] |
Cleavage | Perfect on {001} |
Tenacity | Brittle |
Mohs scale hardness | 3.5–4 |
Luster | Vitreous, pearly on cleavage |
Diaphaneity | Translucent |
Specific gravity | 2.984 |
Optical properties | Biaxial (-) |
Refractive index | nα = 1.592 - 1.595 nβ = 1.624 - 1.625 nγ = 1.625 - 1.627 |
Birefringence | δ = 0.033 |
2V angle | 18° to 28° |
Dispersion | r > v strong |
References | [2][3][4] |
Ephesite is a rare member of the mica silicate mineral group, phyllosilicate. It is restricted to quartz-free, alumina rich mineral assemblages and has been found in South African deposits in the Postmasburg district as well as Ephesus, Turkey.[5]