Anorthoclase
Mineral (Na,K)AlSi3O8
About it
A sodium-rich alkali feldspar of volcanic rocks; rhomb-shaped crystals weather out of lava on Mount Erebus, Antarctica, and it gives the blue shimmer in Norway's larvikite.
- Type
- Mineral
- Group
- Silicate (tectosilicate), feldspar group
- Formula
- (Na,K)AlSi3O8
- Hardness (Mohs)
- 6–6.5
- Specific gravity
- 2.56–2.62
- Streak
- white
- Lustre
- vitreous (glassy), pearly
- Crystal system
- Triclinic
- Colours
- colourless, white, cream, pink, grey
- Transparency
- transparent, translucent
- Cleavage and fracture
- perfect and good in two directions at about 90°
Typical values: real specimens vary. For more, see mindat.org.