Staurolite (Fe₂Al₉(Si,Al)₄O₂₂(OH)₂) is a metamorphic iron-aluminum silicate famous for its cruciform “fairy cross” twin crystals — interpenetrating twin pairs at 90° (Greek cross) or 60° (St. Andrew’s cross) angles. The name comes from Greek “stauros” (cross). Brittany (France) and the Russian Pestrik locality produce the most iconic crosses, while Fannin County (Georgia, USA) supplies abundant collector specimens. Staurolite is a diagnostic indicator of medium-grade regional metamorphism.
Key Facts
- Mohs hardness 7–7.5.
- Monoclinic (pseudo-orthorhombic); prismatic individual crystals.
- Twinning is the diagnostic feature — 90° “Greek cross” and 60° “St. Andrew’s cross” interpenetrant twins.
- Color brown to red-brown to yellow-brown.
- Forms in regional metamorphic mica-schists alongside garnet, kyanite, and andalusite.
Notable Localities
Coray (Brittany, France) — the historical fairy-cross locality. Pestrik (Russia) yields modern Greek-cross twins. Fannin Co. (Georgia, USA) and Taos (New Mexico) supply North American specimens.
Found at these Localities
- Swiss Alps (Alpine-Cleft Province) (瑞士阿尔卑斯高山裂隙矿物产地)
