Grossular

Grossular is a calcium aluminum garnet mineral that ranges in color from colorless to yellow, green, red, or brown. It crystallizes in the cubic system and typically forms dodecahedral or trapezohedral crystals. The mineral has a hardness of 6.5 to 7.5 on the Mohs scale and a specific gravity of approximately 3.6.

The name grossular derives from the Latin word "grossularia," meaning gooseberry, referring to the green variety that resembles the fruit. It was first described in 1792 by German geologist Abraham Gottlob Werner from deposits in the Alps.

Grossular occurs in metamorphic rocks, particularly in contact metamorphosed limestones and skarns. It forms under conditions of moderate to high temperature and pressure, often associated with minerals such as wollastonite, diopside, and vesuvianite. Significant deposits are found in Canada, Russia, Kenya, Tanzania, and the United States.

The mineral exhibits vitreous to resinous luster and can be transparent to translucent. Its refractive index ranges from 1.720 to 1.744, making it optically distinct from other garnet varieties. Under ultraviolet light, some specimens show weak fluorescence.

Grossular has industrial applications as an abrasive material due to its hardness and durability. Fine-grained varieties are used in sandpaper and grinding wheels. The gem-quality specimens, particularly the vivid green tsavorite variety, are prized in jewelry. Tsavorite, found primarily in East Africa, represents one of the most valuable garnet types.

In mineral collections, grossular is valued for its crystal habit and color variations. The hessonite variety, which appears yellow to orange-red, is also popular among collectors. Chemical composition varies slightly depending on the specific deposit, with the general formula Ca3Al2(SiO4)3.