Forsterite - Encyclopedia

    Class : Silicates
    Subclass : Nesosilicates
    Crystal system : Orthorhombic
    Chemistry : Mg₂SiO₄
    Rarity : Very common

Forsterite is the magnesium pole of the olivine group, it is by far the most common mineral in this group and one of the most abundant minerals on the globe. It forms two series, one with fayalite (ferriferous) and the other with tephroite (manganiferous). Forsterite is the fundamental constituent of peridotites, often present in gabbros and basalts and also in certain high-grade metamorphic rocks (dolomitic marble). It was named in honor of Adolarius Jacob Forster, an English mineral merchant. Forsterite crystals are frequently flattened, longitudinally striated, with sharp faces and octahedral terminations, sometimes centimeter-sized. Forsterite is also often in granular masses composed of grains with rounded surfaces, sometimes large. With a glassy luster, it has a characteristic greenish-yellow to green color. It is easily altered to minerals from the serpentine group (chrysotile and antigorite), a phenomenon which can continue with the formation of talc or magnesia. Peridot is the gemmy forsterite, it is used in jewelry, but it is also a highly sought-after industrial mineral for the manufacture of refractories (foundries, ceramics, etc.).

Main photo : Forsterite from Soppat, Manshera, Naran-Kagan Valley, Kohistan, Northwest Frontier, Pakistan

Twins are known on {100}, {011} and {012}.

Synthetic forsterites have been produced in Russian laboratories since 1999. However, the synthetic crystals which are cut for jewelry are blue-violet, a color which does not exist for this species in nature... this synthesis actually aims to imitate the tanzanite...