Staurolite
Mineral Fe2Al9Si4O23(OH)
Also called Cross stone
About it
Brown prisms in mica schist that often twin as crosses at 90 or 60 degrees; fairy crosses come from Georgia and Virginia, and from Brittany, France.
- Type
- Mineral
- Group
- Silicate (nesosilicate), staurolite group
- Formula
- Fe2Al9Si4O23(OH)
- Hardness (Mohs)
- 7–7.5
- Specific gravity
- 3.65–3.83
- Streak
- white to grey
- Lustre
- vitreous (glassy), resinous, dull
- Crystal system
- Monoclinic
- Colours
- brown, red-brown, black
- Transparency
- transparent, translucent, opaque
- Cleavage and fracture
- distinct in one direction
Typical values: real specimens vary. For more, see mindat.org.