Anorthite
Mineral CaAl2Si2O8
About it
The calcium end of the plagioclase series; loose crystals weather out of volcanic ash on Miyake-jima, Japan, and occur at Vesuvius. It makes up much of the Moon's pale highlands.
- Type
- Mineral
- Group
- Silicate (tectosilicate), feldspar group
- Formula
- CaAl2Si2O8
- Hardness (Mohs)
- 6–6.5
- Specific gravity
- 2.74–2.76
- Streak
- white
- Lustre
- vitreous (glassy)
- Crystal system
- Triclinic
- Colours
- white, grey, colourless, reddish
- Transparency
- transparent, translucent
- Cleavage and fracture
- perfect and good in two directions at about 86°
Typical values: real specimens vary. For more, see mindat.org.