Tephroite

Tephroite is a silicate mineral belonging to the olivine group. Its chemical formula is Mn2SiO4, indicating that it is a manganese orthosilicate. It is typically found in manganese-rich metamorphic rocks and in some skarn deposits. Tephroite is characterized by its dark color, which can range from reddish-brown to black, and its vitreous luster. Its hardness on the Mohs scale is between 6 and 6.5, and it has a specific gravity of approximately 4.0. The mineral is relatively rare and often occurs in association with other manganese silicates like rhodonite and rhodochrosite, as well as minerals such as quartz and garnet. Tephroite was first described in 1822 from a locality in Sweden. The name is derived from the Greek word "tephra," meaning ash, referring to its ash-like color. While not a commercially significant mineral, tephroite is of interest to mineral collectors and geologists for its occurrence in specific geological environments and its role in understanding the mineralogy of manganese-rich ore bodies.