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The Mineral Staurolite
staurolite picture

staurolite

staurolite mineral picture

Staurolite is a nesosilicate mineral having a white streak. It is typically opaque and forms crystals in the monoclinic system. Magnesium, manganese and zinc replace in the iron site while trivalent iron can replace aluminum.

Chemical Formula                         
Fe2+2Al9O6 (SiO4) 4 (O, OH) 2

Derivation of Name  
It derives its name from the Greek, “stauros” meaning cross and “lithos”, meaning  stone indicating its common twinning.

Occurrence         
Staurolite is a metamorphic mineral that lies between intermediate and high grade.  It is found with micas, Almandine Garnet, Kyanite in addition to Albite, Sillimanite and Biotite in gneiss and schist of local metamorphic rocks.            

Gemology  
In places where it is available in well formed twinned crystals in the shape of a cross, Staurolite is used for making ornamental jewelry and sold as a memento. However, many such items are not made from genuine, but manufactured crystals. If you come across such items being sold, all of the same shape, size and bubbles within, this could be faked. Its crystals in the shape of a cross are often associated with superstitions and religious beliefs.

 Source 
Georgia State in the US recognizes Staurolite as a state mineral. It is also found in the Alps, Switzerland; Fairy Stone State Park in Patrick County, Virginia. The park is so named due to its local name.  It also occurs in Island Park, Idaho, close to Henry’s lake, Taos; Selbu in Norway and in New Mexico, close to Blanchard Dam in Minnesota.

staurolite mineral

mineral staurolite

Mineralogy  
An extraordinary feature of staurolite is that it is frequently found twinned in a typical cross-shape, known as penetration twinning. Macroscopically visible crystals of staurolite have a prismatic shape. They are frequently bigger than the neighboring minerals and called porphyroblasts.   Thin sections of Staurolite are usually twinned, and demonstrate lower first order birefringence akin to quartz, with the twinning showing optical continuity. It is distinguished in metamorphic rocks due its Swiss cheese facade and frequently mantled porphyroblastic nature.

Color           
Color variation is from deep reddish brown to blackish brown, or yellowish brown, but hardly ever blue; thin sections are of light golden yellow color.                    

Density                              
3.686 g/cm3

Mohs hardness
7 to 7.5

     
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