metamorphic

Staurolite (Fairy Cross)

Staurolite (Fe2+2Al9Si4O23(OH))

AI-generated identification · may be incorrect

Hardness: 7 to 7.5 Mohs; Color: reddish-brown to brownish-black; Luster: vitreous to dull; Crystal structure: monoclinic (pseudo-orthorhombic); Cleavage: distinct in one direction; Specific gravity: 3.7 to 3.8

Hardness: 7 to 7
Color: reddish-brown to brownish-black
Luster: vitreous to dull

Identified March 25, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms during regional metamorphism of clay-rich sedimentary rocks (shales) under intermediate to high pressure and temperature; typically found in mica schists and gneisses.

Uses & applications

Used in the past as an abrasive (sandblasting) due to its hardness; currently primarily used as a geologic 'index mineral' to estimate depth and temperature of metamorphic rocks; popular as a charm or collector's specimen.

Geological facts

Commonly forms 'twinned crystals' where two crystals grow across each other at 90 or 60 degrees, creating a cross shape. It is the official state mineral of Georgia, USA, and folklore suggests they are tears of fairies or cherubs.

Field identification & locations

Identify by its characteristic cross twinning and its presence within a mica schist matrix. Often found in eroded riverbeds or soil near metamorphic belts. Common locations include Fannin County (Georgia), Stuart (Virginia), and parts of the Swiss Alps.