pyropealmandine

Pyropealmandine is a garnet variety that represents a solid solution between the pyrope and almandine endmembers. Garnets have the general formula X3Y2(SiO4)3, where X is a divalent metal and Y is typically Al3+. In the pyrope–almandine series, the X site is principally Mg or Fe, giving endmembers pyrope (Mg3Al2Si3O12) and almandine (Fe3Al2Si3O12). Natural samples commonly display a range of compositions between these ends, described as pyrope-almandine garnet.

Physical properties: Pyrope-almandine garnets are typically red to purplish-red and display the characteristic hardness of garnet, about 6.5 to 7.5 on the Mohs scale. Specific gravity ranges roughly from 3.6 to 4.3, increasing with iron content. They are isometric and usually form dodecahedral crystals; optical properties include a single refractive index without birefringence, as with other garnets.

Geologic occurrence: Pyrope-almandine garnet occurs in metamorphic rocks such as gneiss and schist, particularly in high-temperature, high-pressure environments. It also appears in skarns and in mantle-derived rocks and as heavy mineral grains in sedimentary deposits. The composition and color depend on the Mg–Fe balance, with Mg-rich varieties tending toward pyrope and Fe-rich toward almandine.

Uses and nomenclature: As a member of the garnet group, pyrope-almandine is used as a gemstone when color and clarity are suitable, sold under the broader garnet name. The term is often used in mineralogy and petrology to describe specimens with mixed pyrope and almandine chemistry.