Staurolite in Schist
Staurolite (IMA-approved) in an argillaceous matrix · Mineral Specimen / Collector Mineral
Crystal System
Monoclinic (pseudo-orthorhombic); typically forms prismatic crystals often twinned in 60-degree or 90-degree crosses.
Mineral Group
Silicates (Nesosilicates)
Chemical Formula
Fe2+2Al9Si4O23(OH)
Formation Process
Metamorphic; forms under medium-grade regional metamorphism of aluminum-rich sedimentary rocks (pelites) at specific temperature/pressure ranges.
About This Crystal
Dark reddish-brown to black opaque crystals embedded in a lighter, sandy or micaceous matrix. The crystals display a dull to vitreous luster and distinct blocky forms.
Physical Characteristics
Color: Dark brown; Streak: White to grayish; Cleavage: One distinct but poor; Fracture: Subconchoidal; Specific Gravity: 3.7 - 3.8; Non-fluorescent.
Optical Properties
Biaxial (+); Refractive Index: 1.739–1.761; Pleochroism: Strong (colorless to yellow to reddish-brown); Singly refracting in appearance due to opacity.
Hardness & Durability
Origin Region
Common in metamorphic belts such as Fannin County (Georgia, USA), Brittany (France), and the Kola Peninsula (Russia).
Hardness & Durability
7 to 7.5 on Mohs scale; brittle toughness; generally stable but can be prone to breaking along twin planes.
Care & Maintenance
Clean with warm soapy water and a soft brush; avoid ultrasonic cleaners which may shatter the matrix; store away from harder stones to prevent scratching.
Rarity & Value
Relatively common; value is determined by the perfection of the 'cross' twinning. Most specimens are inexpensive unless perfectly formed natural crosses.
Special Characteristics
Renowned for penetration twinning, forming 'Fairy Crosses' at 90-degree (Greek cross) or 60-degree (St. Andrew’s cross) angles.
Lore & History
Historically known as 'Fairy Stones' or 'Fairy Crosses' in Appalachian folklore; traditionally used as good luck charms and believed to provide grounding and protection.