Silicates: Orthopyroxene (Enstatite-Hypersthene)

Composition: (Mg,Fe)SiO₃; the name enstatite is used for the magnesium-rich variety and the name hypersthene for the iron-rich variety

Crystal system: Orthorhombic; usually irregular grains or cleavable masses

5.20.1
cleavable enstatite altering to serpentine
Norway

Properties:

• Vitreous lustre
• Variable color; usually pale green green to dark brown
• White to grey streak
• Knife does not scratch (Mohs Hardness 6)
• Above average density depending on iron content
• Two cleavages at right angles to each other
• Cleaves rather than fractures
• Not ferromagnetic
• Does not react with hydrochloric acid (HCl)

Occurrence:

The orthopyroxenes occur in many mafic igneous rocks and some high grade metamorphic rocks. Specialised characterisation is usually necessary to distinguish among the pyroxene minerals.

5.20.2
cleavable enstatite altering to serpentine
Norway