metamorphic
Fairy Stone (Staurolite Concretion)
Staurolite (Fe2+2Al9Si4O23(OH))
Hardness: 7-7.5 on Mohs scale; Color: Dark brown, reddish-brown, or brownish-black; Luster: Vitreous to dull/earthy; Crystal Structure: Monoclinic (often forming cruciform twins); Cleavage: Distinct; Specific Gravity: 3.74-3.83.
- Hardness
- 7-7
- Color
- Dark brown, reddish-brown, or brownish-black
- Luster
- Vitreous to dull/earthy
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Physical properties
Hardness: 7-7.5 on Mohs scale; Color: Dark brown, reddish-brown, or brownish-black; Luster: Vitreous to dull/earthy; Crystal Structure: Monoclinic (often forming cruciform twins); Cleavage: Distinct; Specific Gravity: 3.74-3.83.
Formation & geological history
Formed during regional metamorphism of clay-rich sedimentary rocks (shales). Predominantly found in metamorphic schists and gneisses, often associated with garnet and kyanite. The specimen in the image appears to be a weathered cross-twin or concretionary cluster.
Uses & applications
Primarily used as a collector specimen and in jewelry (pendants/charms). Historically used as a talisman or good luck charm. It has minor industrial use as an abrasive in sandblasting.
Geological facts
Known as 'Fairy Stones' due to legends suggesting they are the solidified tears of fairies. They naturally grow in 'cross' shapes due to a phenomenon called twinning, where two crystals grow together at 60 or 90 degree angles.
Field identification & locations
Identify in the field by looking for distinct 60-degree or 90-degree 'X' or '+' shaped dark crystals protruding from a softer mica schist matrix. Common in Patrick County, Virginia, and parts of Georgia and North Carolina.
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