Staurolite

Iron Aluminum Silicate Hydroxide
Fe₂Al₉Si₄O₂₂(OH)₂

A special property of staurolite is that it often occurs twinned in a characteristic cross-shape.

The History Says

Staurolite was the regional metamorphic mineral of Greek from intermediate to high grade. From Greek the name has been derived. There 'stauros' mean cross, as is referred to the common twinning of the mineral.

The Present Scenario

Staurolite is the official state mineral of Georgia.

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Staurolite is a common metamorphic mineral, being useful to geologists in determining the degree of metamorphism. It is famous because of its twinned crystals which forms the shape of a cross. The name has been derived from Greek word "stauros," which mean a cross.

The twin is a classic penetration twin. It appears like two crystals grew into and out of each other. In fact, it forms two twin types. One of them is nearly 90 degrees and the other, nearly 60 degrees. The most sought and common is the 60 degree type.

It was associated with Christianity, for the symbol cross and as a good luck charm. It is also called "Fairy Stone" or "Fairy Cross." Some of the scarcer specimens show both the twin forms and can really look like a blunt six rayed star.

Physical Properties of Staurolite

Color	Reddish-brown, brown, and black.
Luster	Vitreous to resinous to dull.
Transparency	Crystals are translucent to opaque.
Crystal system	Monoclinic, 2/m
Crystal habits	Prismatic or tabular. Some may have a psuedo-hexagonal cross-section but most of them are flattened into a more (+) or X-shaped and can be both at the same time. Crystals are sometimes grown onto kyanite crystals.
Cleavage	Poor, in one direction.
Fracture	Uneven to conchoidal.
Hardness	7 - 7.5
Specific gravity	3.7 - 3.8
Streak	White

Associated Minerals of Staurolite

• Almandine
• Micas
• Kyanite
• Other metamorphic minerals

Occurrences of Staurolite

• Ducktown Tennessee, Georgia, Virginia and Montana, USA
• Brazil
• Scotland
• Italy
• France