pyropes

Pyropes are magnesium aluminum silicate garnets, with the end-member formula Mg3Al2Si3O12. They belong to the garnet group and form solid-solution series with other garnets such as almandine and spessartine. The name comes from the fiery red color often observed in pyrope specimens, from the Greek pyros (fire) and ops (eye).

Geologic occurrence: Pyrope-rich garnets form under high-temperature metamorphic conditions and are common in granulite and eclogite facies rocks, as well as in mantle xenoliths brought to the surface by kimberlites. They occur worldwide in metamorphic belts and ultramafic rocks and are frequently associated with other garnet varieties, including almandine and grossular.

Physical properties: Pyrope garnets are typically red to purplish red, transparent to translucent, and have a vitreous luster. Crystals are isometric and commonly form dodecahedra or trapezohedra. Typical hardness is about 7 on the Mohs scale, with densities in the mid-3.5 to 3.9 g/cm3 range.

Uses and significance: Pyrope garnets are collected as gemstones and used in jewelry, especially in colors ranging from deep red to pink. In geology, the magnesium-rich end-member content of garnet is used in geothermobarometry to infer metamorphic temperatures and pressures, helping to reconstruct the conditions of metamorphism and mantle processes.