Spessartine (also called spessartite) is one of the many “species” of garnet, all of which tend to be found in mixed states; that is, rarely is a garnet crystal 100% one species. Instead, they are usually a mix. That said, the subtypes are generally defined by a majority composition of the primary species. Spessartine is a manganese-aluminum garnet; the manganese gives it the orange colors that fine spessartines are prized for (although they can range from a brilliant yellow-orange to a dark red-orange). They are typically included with fine small crystals or bubbles. These inclusions are referred to as “sugar” and can give the garnet a soft glow in the hand that is difficult to capture in a photo. The gems are rarely very large, particularly in the finest orange colors but they are very brilliant due to a high refractive index of 1.789 to 1.820 as well as a relatively high dispersion value of 0.027. With a Mohs hardness of 7-7.5, its a durable gemstone.
While some refer to the orange spessartines from Nambia as “mandarin garnets,” this is in fact a color range and not at true variety. Similar mandarin-orange spessartine has been found at other locations.
Where is it found
Until recently the primary source for gem-grade spessartine garnet was the Little Three Mine and Hercules Mine in Ramona, California. In the last decade, significant finds in Namibia, Tanzania and Nigeria have eclipsed the California mines, and in fact the California mines are now closed. While spessartine is a very common garnet, gem-grade spessartine remains relatively rare.
Spessartine is not treated.
Use in jewelry
The brilliance and hardness of spessartine make a great choice for jewelry, especially as its one of the few orange gemstones. The finds in Africa in the last 10-15 years have substantially increased the amount of this once rare gemstone in the market. While one might think that prices have declined, in fact they have increased–its just common enough to support a market with significant demand, but not common enough to meet all of the demand created. Generally the most expensive spessartines are the rich mandarin oranges and the deep burnt orange/red gems.
You can look at my current inventory of loose gemstones online here: http://www.earthstreasury.com/product-category/gemstones/garnet/spessartite/