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Spessartite Mineral Facts:

Chemical Formula: Mn3Al2(SiO4)3
Manganese aluminum garnet. Ferrous iron often replaces the manganese and ferric iron some of the aluminum. The name is taken from the city of Spessart, a locality in German Bavaria where this type of garnet was first identified. Also known as Spessartine garnet.

Colors: Deep orange to brownish red.
The purest specimens of this manganese aluminum garnet, with little iron content are a light yellow orange color. The darkest specimens generally contain the highest amounts of iron.

Hardness: 7

Density: about 3.8

Cleavage: None

Crystallography: Isometric, hexoctahedral
Usually distinctly crystallized; also in rounded grains. When crystalized, commonly forms dodecahedron and trapezohedron, often in combination. Hexoctahedron observed at times.

Luster:. Vitreous glassy luster. It is transparent or translucent. The streak is always white or whitish, and the fracture subconchoidal or

Optics: (Refractive Index):  = 1.8105

Spessartite garnel with albite and schorl

spessartite garnet on albite feldspar

Composition, Structure and Associated Minerals:
Spessartite is found in acid igneous rocks and in various schist formations. The largest and finest specimens, including nearly all gem quality material are found in granitic pegmatites where it is associated with albite feldspar, tourmaline and various mica minerals. Spessartite also occurs in the igneous rock, rhyolite where it is found in the lithophyse cavities in that rock. Spessartine from Rhyolite can make some very well formed specimens, but the color is normally very dark, ranging from dark red -brown to dark violet red.

Spessartite is hyacinth or orange red, with occasionally a tinge of brown or violet. The purest varieties are yellow, but since there is nearly always an admixture of one of the iron molecules, the more usual color, is reddish orange. Those with a larger almandine content are more reddish, to red brown in hue. The mineral is usually transparent.

Identification and Diagnostics
Spessartite when fused with sodium carbonate gives a bluish green bead (positive test for manganese). In the blowpipe flame it fuses fairly easily to a black, nonmagnetic mass. Garnets, when in crystals, are easily distinguished from other similarly crystallizing substances by their characteristic isometric crystals, color and hardness, etc. Massive garnet may resemble vesuvianite, sphene, zircon or tourmaline. It is distinguished from zircon by its easier fusibility and from vesuvianite by its more difficult fusibility; from tourmaline by its higher specific gravity, and from sphene by the reaction from titanium. It frequently requires a chemical analysis to positively distinguish between the different members of the garnet group, or the percentages of each molecule in an individual specimen

spessartite garnet

Occurrence, Localities and Origins:
Its principal known occurrences are in Brazil and Africa. In both locations the mineral is mined from pegmatites. Its best known occurrences in the United States are in granite, at Haddam, Conn., in pegmatite, at Amelia Court House, Virginia, and near Ramona in San Diego County, California. It is also found in the lithophyse of rhyolites, near Nathrop, in Colorado, in Maine, and near Ely, Nevada, where it forms as the product of pneumatolitic processes, in openings lined with tridymite silica. The location near Ely is known as Garnet Hill and is a well known rock hound location which is open to the public. Breaking open the pink to gray rhyolite yields small crystals of spessartine garnet, and nice specimens are not especially difficult to acquire. Spessartine from garnet in rhyolite cavities in normally very dark colored, and while quite suitable for attractive mineral collector specimens, is too dark in color for any gem usage.

It is among the rarer forms of garnet, and sees only a little gemstone use in spite of its beauty and high refractive index. Gems from Brazil or Africa are sometimes offered for sale. They tend to be smaller in size that some other garnet gems. Its specimens can be well formed and large, so the better ones are much valued and appreciated by mineral collectors.

Return to the Mineral Collectors Information Page

Garnet Hill Spessartine, Ely, Nevada

Spessartite from Ramona, California Spesartine Garnet Crystal, Brazil

Spesartine Garnet Crystal, Brazil



Please note that the author, Chris Ralph, retains all copyrights to this entire document and it may not be reproduced, quoted or copied without permission.

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