metamorphic
Staurolite (Fairy Stone)
Staurolite (formula: Fe2+2Al9Si4O23(OH))
Hardness: 7 to 7.5 on Mohs scale; Color: Reddish brown to brownish black; Luster: Vitreous to dull/earthy; Crystal structure: Monoclinic (pseudo-orthorhombic); Specific gravity: 3.7 to 3.8; Cleavage: Poor.
- Hardness
- 7 to 7
- Color
- Reddish brown to brownish black
- Luster
- Vitreous to dull/earthy
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Physical properties
Hardness: 7 to 7.5 on Mohs scale; Color: Reddish brown to brownish black; Luster: Vitreous to dull/earthy; Crystal structure: Monoclinic (pseudo-orthorhombic); Specific gravity: 3.7 to 3.8; Cleavage: Poor.
Formation & geological history
Formed through regional metamorphism of pelitic rocks (shales and mudstones) under medium temperature and pressure. Common in schists and gneisses ranging from the Paleozoic to Precambrian eras.
Uses & applications
Primarily collected as mineral specimens; higher quality 'cross' twins are used in religious jewelry or as folk talismans. Occasionally used as an abrasive or as an index mineral for geological mapping.
Geological facts
Famous for its cruciform twinning, where two crystals grow together at 60 or 90-degree angles to form a cross. Legends in Virginia claim they are the crystallized tears of fairies who wept upon hearing the news of Christ's death.
Field identification & locations
Identify in the field by looking for distinct 60-degree (St. Andrew's cross) or 90-degree (Greek cross) twinning in mica schists. Commonly found in Fannin County (Georgia), Patrick County (Virginia), and the Taos mountains (New Mexico).
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