![]() | This article is largely based on an article in the out-of-copyright Encyclopædia Britannica Eleventh Edition, which was produced in 1911. (November 2019) |
Epidote | |
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General | |
Category | Sorosilicates |
Formula (repeating unit) | {Ca2}{Al2Fe3+}(SiO4)(Si2O7)O(OH) |
IMA symbol | Ep[1] |
Crystal system | Monoclinic |
Crystal class | Prismatic (2/m) (same H–M symbol) |
Space group | P21/m |
Identification | |
Color | Pistachio green, yellow-green, greenish black, brownish-green, green, black |
Crystal habit | Prismatic with striations, fibrous, massive |
Twinning | On [100] |
Cleavage | {001} perfect and {100} imperfect |
Fracture | Flat regular to uneven |
Mohs scale hardness | 6–7 |
Luster | Vitreous to resinous |
Streak | Greyish white |
Diaphaneity | Transparent to nearly opaque |
Specific gravity | 3.38–3.49 |
Optical properties | Biaxial (-) |
Refractive index | nα = 1.715–1.751 nβ = 1.725–1.784 nγ = 1.734–1.797 |
Birefringence | δ = 0.019–0.046 |
Pleochroism | Strong |
References | [2][3][4] |
Epidote is a calcium aluminium iron sorosilicate mineral.