Ferrosilit

Ferrosilit, also spelled ferrosilite in English, is the iron end-member of the orthorhombic pyroxene group, with chemical composition FeSiO3. It forms a solid-solution series with enstatite (MgSiO3) and is a constituent of the orthopyroxene subgroup of the pyroxene minerals.

Crystal chemistry and occurrence are typical of orthopyroxenes. Ferrosilit is usually described as part of igneous and metamorphic rock assemblages that are enriched in iron. It occurs in ultramafic rocks and in high-temperature metamorphic rocks, and can be found in some meteorites as well. In rocks, it commonly appears together with enstatite, diopside, or other pyroxenes, reflecting varying iron-magnesium ratios.

Physical properties and identification are characteristic of pyroxenes. Ferrosilit is typically dark brown to black, with a vitreous to submetallic luster. It has a Mohs hardness around 5 to 6 and exhibits two good cleavage planes at near 90 degrees, a hallmark of pyroxenes. Crystals are usually prismatic, though in rocks it is often found as intergrown grains.

Significance and notes. Ferrosilit provides information about the iron content and tectono-metamorphic conditions of rocks. Its presence helps distinguish orthopyroxene-rich assemblages from those dominated by magnesium-rich enstatite or calcium-rich clinopyroxenes, aiding interpretation of a rock’s formation environment and thermal history.