spessartite

Spessartine, or spessartite garnet, is a mineral species in the garnet group with the chemical formula Mn3Al2Si3O12. It is the manganese-rich endmember of the pyrope-almandine-spessartine garnet series and occurs in solid solution with other garnet endmembers. In gemstone use, spessartine is valued for its orange to red-orange colors.

The name derives from the Spessart region in Germany, where the mineral was first described in the 19th century. Spessartine forms in metamorphic rocks, particularly aluminous schists and granulites, and in granitic pegmatites. It is commonly associated with other garnets, quartz, kyanite, and sillimanite. Notable sources include the Spessart region, as well as Namibia, Tanzania, Madagascar, Sri Lanka, Afghanistan, and the United States.

Physically, spessartine crystals are typically transparent to translucent and display a color range from orange to reddish-orange. The orange hue is largely due to manganese. Garnets in general have a high refractive index and dispersion, contributing to their brilliance, and spessartine shares these optical traits. It is relatively hard, with a Mohs hardness around 6.5 to 7.5, and a specific gravity roughly in the mid-range for garnets. Cleavage is poor to none, and the mineral commonly exhibits a vitreous luster.

As a gemstone, spessartine is prized for its vivid color, and the bright orange stones from some deposits are marketed as Mandarin garnet. While many stones occur naturally with desirable coloration, some specimens may be heat-treated to intensify color in the trade.

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