metamorphic
Staurolite
Staurolite (Fe2+2Al9Si4O23(OH))
Hardness: 7-7.5 (Mohs scale); Color: Dark brown, reddish-brown, or brownish-black; Luster: Vitreous to resinous (dull when weathered); Crystal structure: Monoclinic (often appears orthorhombic); Cleavage: Moderate in one direction; Specific Gravity: 3.7 to 3.8
- Hardness
- 7-7
- Color
- Dark brown, reddish-brown, or brownish-black
- Luster
- Vitreous to resinous (dull when weathered)
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Physical properties
Hardness: 7-7.5 (Mohs scale); Color: Dark brown, reddish-brown, or brownish-black; Luster: Vitreous to resinous (dull when weathered); Crystal structure: Monoclinic (often appears orthorhombic); Cleavage: Moderate in one direction; Specific Gravity: 3.7 to 3.8
Formation & geological history
Formed during regional metamorphism of pelitic rocks (shales and mudstones) under medium to high pressure and temperature conditions. It typically occurs in schists and gneisses alongside garnet and kyanite.
Uses & applications
Commonly used as an abrasive in sandblasting and water-jet cutting due to its high hardness. Also highly valued by mineral collectors, especially specimens showing characteristic 'cross' twin crystals (Fairy Stones).
Geological facts
Known as the 'Fairy Stone' or 'Fairy Cross' because it frequently forms cruciform twins at 60 or 90-degree angles. Legend claims these were formed from the tears of fairies who wept after hearing the news of the death of Christ.
Field identification & locations
Identify in the field by its characteristic dark brown color, high hardness (will scratch glass), and prism-like or cross-shaped crystals within a mica schist matrix. Common locations include Georgia and Virginia (USA), Switzerland, and Russia.
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