Oligoclase
Mineral (Na,Ca)(Si,Al)4O8
Also called Aventurine feldspar
About it
Plagioclase with 10 to 30 per cent calcium, showing twin striations on cleavage faces. Glittering orange sunstone from Norway and India is oligoclase spangled with hematite flakes.
- Type
- Mineral
- Group
- Silicate (tectosilicate), feldspar group
- Formula
- (Na,Ca)(Si,Al)4O8
- Hardness (Mohs)
- 6–6.5
- Specific gravity
- 2.64–2.66
- Streak
- white
- Lustre
- vitreous (glassy), pearly
- Crystal system
- Triclinic
- Colours
- white, grey, greenish, yellowish, colourless, orange
- 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.