Staurolite
Real mineral · uncommon · Fe₂²⁺Al₉O₆(SiO₄)₄(O,OH)₂
Forms penetration twins in characteristic cross shapes at approximately 60 or 90 degrees. Found in medium-grade metamorphic schists alongside garnet and kyanite. Used as an indicator of moderate metamorphic pressure and temperature.
Identity
- Formula
- Fe₂²⁺Al₉O₆(SiO₄)₄(O,OH)₂
- Chemical class
- silicate
- Also known as
- Fairy cross (cross-shaped twins), Fairy stone
Crystallography
- Crystal system
- monoclinic
- Habits
- prismatic, massive
- Fracture
- subconchoidal
Physical properties
- Mohs hardness
- 7
- Density
- 3.74 g/cm³
- Luster
- vitreous, resinous
- Colors
- reddish brown, dark brown, brownish black
- Streak
- white to gray
- Transparency
- opaque, translucent
Geology
- Origins
- metamorphic
- Host rocks
- schist, gneiss
- Associated minerals
- Kyanite, Garnet, Mica, Quartz
- Geography
- USA, Russia, France, Switzerland, Brazil
Classification
- Rarity
- uncommon
- Gem quality
- No
Arcane properties
- Affinity
- earth, light
- Effects
- warding
- Planar origin
- Material Plane
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