metamorphic
Staurolite (Fairy Stone)
Staurolite (Fe2+2Al9Si4O23(OH))
Hardness: 7 to 7.5 on Mohs scale; Color: Reddish brown to dark brown or brownish-black; Luster: Vitreous to dull; Crystal Structure: Monoclinic (often forming prismatic crystals and distinctive 60/90 degree twins); Cleavage: Distinct in one direction; Specific Gravity: 3.74 to 3.83
- Hardness
- 7 to 7
- Color
- Reddish brown to dark brown or brownish-black
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 to 7.5 on Mohs scale; Color: Reddish brown to dark brown or brownish-black; Luster: Vitreous to dull; Crystal Structure: Monoclinic (often forming prismatic crystals and distinctive 60/90 degree twins); Cleavage: Distinct in one direction; Specific Gravity: 3.74 to 3.83
Formation & geological history
Formed through regional metamorphism of aluminous sediments (shales). It typically occurs in schists and gneisses of the Paleozoic or Precambrian age, forming under medium temperatures and pressures.
Uses & applications
Used primarily as an abrasive sand in sandblasting and water-jet cutting. Well-formed twinned crystals are popular for mineral collecting and are sometimes used as religious or good-luck charms in jewelry.
Geological facts
Commonly known as 'Fairy Stones' or 'Fairy Crosses' because the crystals frequently twin to form the shape of a cross. Legend in the Blue Ridge Mountains suggests they are the solidified tears of fairies who wept when they heard of Christ's death.
Field identification & locations
Identify in the field by its characteristic brown color, extreme hardness relative to the surrounding mica schist, and its cross-like or hexagonal crystal shapes. Frequently found in Virginia (Patrick County), Georgia, and the Alps.
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