Sanidine
Mineral (K,Na)AlSi3O8
Also called Glassy feldspar
About it
The high-temperature potassium feldspar of rhyolite and trachyte: clear, glassy tabular crystals, often Carlsbad twins. Known from the Eifel and Drachenfels, Germany.
- Type
- Mineral
- Group
- Silicate (tectosilicate), feldspar group
- Formula
- (K,Na)AlSi3O8
- Hardness (Mohs)
- 6
- Specific gravity
- 2.56–2.62
- Streak
- white
- Lustre
- vitreous (glassy)
- Crystal system
- Monoclinic
- Colours
- colourless, white, grey, yellowish
- Transparency
- transparent, translucent
- Cleavage and fracture
- perfect and good in two directions at 90°
Typical values: real specimens vary. For more, see mindat.org.