Staurolite

Physical Properties

Hardness: 7-7.5 (Mohs scale), Color: Reddish-brown to brownish-black, Luster: Vitreous to dull, Crystal structure: Monoclinic (pseudo-orthorhombic), Cleavage: Distinct in one direction, Specific gravity: 3.74–3.83.

Formation & Geological History

Formed through regional metamorphism of pelitic rocks (shales and mudstones) under medium to high pressure and temperature conditions. Typically found in mica schists and gneisses.

Uses & Applications

Used primarily as a metamorphic index mineral for geologists to determine metamorphic grade. Sometimes used as a gemstone when transparent, or sold as 'Fairy Stones' when twinned.

Geological Facts

Staurolite is famous for forming 'cruciform' twins where two crystals cross each other. In folklore, these are called 'Fairy crosses' or 'Fairy stones' and were historically carried for good luck.

Field Identification & Locations

Identify by its blocky prismatic shape and brown color. It is harder than the surrounding mica in schist, often standing out in relief. Commonly found in the Appalachian Mountains, USA (especially Georgia and Virginia), and the Alps.

Identified on: 4/20/2026

Mode: Standard