Silicates: Augite

Composition: Ca(Na,Mg,Fe,Mn,Al,Ti)₂(Si,Al)₂O₆; augite includes some aluminium, whereas diopside-hedenbergite are aluminium-poor varieties

Crystal system: Monoclinic; prismatic crystals often nearly square in cross section, also massive and granular forms

5.4.1
diopside with calcite
Mt Frosty mine
north west Qld Australia

Properties:

• Vitreous lustre
• Variable color; usually dark green to black
• 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:

Pyroxenes including augite occur in medium and high grade metamorphic rocks, many igneous rocks and some hydrothermal replacement ore deposits. Specialised characterisation is usually necessary to distinguish among the pyroxene minerals.

5.4.2
hedenbergite
Broken Hill NSW Australia