Spessartin

Spessartin, commonly called spessartine garnet and historically named spessarite, is a manganese-rich garnet species and a member of the garnet group. It is the manganese endmember with the chemical formula Mn3Al2Si3O12, crystallizing in the isometric system. The color is typically orange to reddish-orange, sometimes brownish, with the hue governed by Mn2+ content.

In terms of physical properties, spessartin has a Mohs hardness of about 6.5–7.5, a specific gravity around 4.0–4.3, and a refractive index within the garnet range. Garnets are isotropic minerals, so spessartin shows no pleochroism.

Spessartin forms in metamorphic rocks such as mica schists and granulites, and in granitic pegmatites. Economically important gem-quality material has been found in the Spessart forest region of Germany, after which the variety is named, as well as in Madagascar, Namibia, Pakistan, Tanzania, and Brazil. It commonly occurs with other garnets, such as almandine and pyrope, and with minerals like quartz, biotite, and kyanite.

In jewelry, spessartin is valued as a gemstone for its bright orange to orange-red color, durability, and clarity. It is cut into faceted stones and also collected as mineral specimens. Treatments are uncommon; heat treatment can alter color in some garnets, but is less typical for spessartin.