Omphacite

Omphacite is a member of the pyroxene 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 pyroxene. Omphacite compositions are intermediate between calcium-rich augite and sodium-rich jadeite. It crystallizes in the monoclinic system with prismatic, typically twinned forms, though usually anhedral. Its space group (P2/n) is distinct from that of augite and jadeite (C2/c). 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.
See more at Wikipedia.org...

General Information:
 Chemical Formula:
(Ca,Na)(Mg,Fe++,Fe+++,Al)Si2O6
 IMA Status:
Approved IMA 1987
Physical Properties:
 Cleavage:
[110] Good
 Color:
grass green or dark green.
 Density:
3.29 - 3.39, Average = 3.34
 Diaphaniety:
Translucent
 Hardness:
5-6 - Between Apatite and Orthoclase
 Luster:
Vitreous - Silky
 Streak:
greenish white
More details...