Staurolite

Formula: Fe2+2Al9O6(SiO4)4(O,OH)2Mohs scale hardness: 7-7,5Specific gravity: 3.74 - 3.83 meas. 3.686 calc.Staurolite is a red brown to black, mostly opaque. Magnesium, zinc and manganese substitute in the iron site and trivalent iron can substitute for aluminium. Staurolite often occurs twinned in a characteristic cross-shape, called cruciform penetration twinning. Staurolite is a regional metamorphic mineral of intermediate to high grade. It occurs with almandine garnet, micas, kyanite; as well as albite, biotite, and sillimanite in gneiss and schist of regional metamorphic rocks. It is the official state mineral of the U.S. state of Georgia and is also to be found in the Lepontine Alps in Switzerland. Staurolite is also found in Fairy Stone State Park in Patrick County, Virginia. The park is named for a local name for staurolite from a legend in the area. Samples are also found in Island Park, Idaho, near Henrys Lake; Taos, New Mexico; near Blanchard Dam in Minnesota; and Selbu, Norway.References

  1. https://en.wikipedia.org

  2. https://en.wikipedia.org/wiki/Staurolite