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.
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
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