Pumpellyite-(Mg)
Mineral Ca2MgAl2(SiO4)(Si2O7)(OH)2·H2O
Also called Pumpellyite and Isle Royale greenstone
About it
Green fibrous mineral of low-grade metamorphosed basalt; chatoyant "turtle-back" pebbles from Isle Royale and Michigan's Keweenaw, called chlorastrolite, are Michigan's state gem.
- Type
- Mineral
- Group
- Silicate (sorosilicate), pumpellyite group
- Formula
- Ca2MgAl2(SiO4)(Si2O7)(OH)2·H2O
- Hardness (Mohs)
- 5–6
- Specific gravity
- 3.1–3.3
- Streak
- white
- Lustre
- vitreous (glassy), silky
- Crystal system
- Monoclinic
- Colours
- blue-green, green, olive green, brown
- Transparency
- transparent, translucent
- Cleavage and fracture
- distinct in one direction
Typical values: real specimens vary. For more, see mindat.org.