Augite
Mineral (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6
About it
Black, stubby eight-sided prisms common in basalt and gabbro; loose crystals weather out of volcanic ash at Etna and Vesuvius. Told from hornblende by its right-angle cleavages.
- Type
- Mineral
- Group
- Silicate (inosilicate), pyroxene group
- Formula
- (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6
- Hardness (Mohs)
- 5.5–6
- Specific gravity
- 3.19–3.56
- Streak
- greenish grey
- Lustre
- vitreous (glassy), dull
- Crystal system
- Monoclinic
- Colours
- black, dark green, brown
- Transparency
- transparent, translucent, opaque
- Cleavage and fracture
- good in two directions at nearly 90°
Typical values: real specimens vary. For more, see mindat.org.