Clinoenstatite

Formula: Mg2Si2O6 inosilicate (chain silicate) pyroxene
Specific gravity:
Hardness: 5 to 6
Streak: White
Colour: Colourless, greenish yellow, yellowish brown, green-brown
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Environments:

Plutonic igneous environments

Alteration

forsterite and anorthite to clinoenstatite, diopside and spinel
2Mg2SiO4 + CaAl2Si2O8 ⇌ 2MgSiO3 + CaMgSi2O6 + MgAl2O4
The reaction can proceed in either direction, depending on the ambient conditions.

Common impurities: Ti,Al,Cr,Fe,Mn,Ca,Na