Johannsenite

Silicate mineral in the pyroxene family. It has a molecular formula of Ca(Mn,Fe)Si2O6. A calcium-manganese-iron silicate mineral, johannsenite is produced either by metamorphic processes in altered limestones or is associated with pyrite or other minerals in copper, lead, and zinc ores. It is moderately hard, has a glassy lustre, and forms brown, gray, or green crystals