Silicates: Staurolite

Composition: (Fe,Mg)₂(Al,Fe)₉Si₄O₂₂(O,OH)₂

Crystal system: Orthorhombic; prismatic crystals commonly twinned to form cross at 90^o or 60^o

5.27.1
staurolite crystals in mica schist
north west Qld Australia

Properties:

• Vitreous to resinous lustre
• Brown to black color
• Grey streak
• Knife does not scratch (Mohs Hardness 7)
• Above average density
• Cleavage rarely apparent
• Uneven fracture
• Not ferromagnetic
• Does not react with hydrochloric acid (HCl)

Occurrence:

Staurolite occurs in regional metamorphic rocks and also in heavy mineral sand deposits .

5.27.2
staurolite crystals in mica schist
north west Qld Australia