metamorphic
Staurolite (Fairy Stone)
Staurolite (Fe2+2Al9Si4O23(OH))
Hardness: 7-7.5 on Mohs scale; Color: Reddish brown, dark brown, to brownish-black; Luster: Vitreous to resinous; Crystal structure: Monoclinic (pseudo-orthorhombic); Cleavage: Distinct; Specific gravity: 3.7 to 3.8.
- Hardness
- 7-7
- Color
- Reddish brown, dark brown, to brownish-black
- Luster
- Vitreous to resinous
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Physical properties
Hardness: 7-7.5 on Mohs scale; Color: Reddish brown, dark brown, to brownish-black; Luster: Vitreous to resinous; Crystal structure: Monoclinic (pseudo-orthorhombic); Cleavage: Distinct; Specific gravity: 3.7 to 3.8.
Formation & geological history
Formed during regional metamorphism of aluminous rocks like shale. It typically occurs in schists and gneisses. Geological age varies by location, often associated with ancient mountain-building events.
Uses & applications
Primary use is as a gemstone or collector's specimen. In industry, it was historically used as an abrasive (sandblasting) due to its hardness, though synthetic materials are now more common.
Geological facts
Known as 'Fairy Stones' or 'Fairy Crosses' due to its tendency to form cruciform twins (cross-shapes). It is the official state mineral of Georgia, USA. Folklore suggests they were formed from the tears of fairies.
Field identification & locations
Identify in the field by its distinct prismatic crystal habit and common 'X' or '+' shape twinning. They are frequently found weathered out of soft schist. Common locations include Virginia, Georgia, and New Mexico in the USA, as well as Brazil and Russia.
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