Glaucophane
Mineral Na2(Mg3Al2)Si8O22(OH)2
About it
Lavender-blue to grey-blue prisms that colour blueschist, a rock formed at high pressure in subduction zones; known from California's Franciscan rocks, Île de Groix in France, and the Alps.
- Type
- Mineral
- Group
- Silicate (inosilicate), amphibole group
- Formula
- Na2(Mg3Al2)Si8O22(OH)2
- Hardness (Mohs)
- 6–6.5
- Specific gravity
- 3.07–3.15
- Streak
- bluish grey
- Lustre
- vitreous (glassy), pearly
- Crystal system
- Monoclinic
- Colours
- blue, lavender blue, grey-blue
- Transparency
- transparent, translucent
- Cleavage and fracture
- perfect in two directions at about 56° and 124°
Typical values: real specimens vary. For more, see mindat.org.