Gem of the Month

Each month this section will feature either a topic of interest to gem lovers or one special gemstone with background on the material and its value.

Go to: Homepage -- what's new at ACS -- monthly specials and discounts -- "buried treasures" -- BWS/FS jewelry designs -- gem topic of the month -- gem topic archive -- birthstones -- ask Barbara -- key to all the codes used on the ACS site -- definitions of terms used on the ACS site -- how to order -- about ACS -- setting these gems -- free gemology course

 

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Spessartite Garnet

(Thanks to Barry Bridgestock for some of the text and photos in this essay)

Named for Spessart, in NW Bavaria, Germany, this orangey, lustrous garnet variety is not well known outside of gemological circles. Ranging from red to reddish orange to orange to orangey yellow to orangey brown this variety is the manganese aluminum silicate member of a solid solution series of garnets. In general, the less iron which is present in the crystal structure the lighter and purer orange the color will be. With a higher refractive index and polish luster than most of the garnet group, a clean, well polished specimen of this variety is a delight to the eye.

[Typical range of Spessartite colors: near pure red, orange/red, yellow orange, orangey brown]

Some of the most beautiful Spessartites came from Ramona, California in the late 19th and early 20th century. As of 2001 the Spessartite Mine was being worked again, prompting an excellent article to be written for the Winter, 2001 issue of  "Gems and Gemology" on Spessartite characteristics, occurence and mining techniques. Often small, but well formed crystals and crystal clusters occur which are tempting to collectors and jewelry designers.

[Spessartite crystals from Ramona, California: Image courtesy of Barry Bridgestock, and a cluster from China]

There are numerous deposits world wide, but in today's market the Nigerian and Nambian stones command the highest prices and the greatest admiration. The Namibian stones are the purest orange and have been given the trade name "Mandarin" by their promoter. As lovely as they are, the typical stone is under one carat and may be included. A recent find of gem quality Spessartite in Nigeria has provided the world with larger, cleaner stones that are have just slightly less orangey purity than the Namibian pieces.

[Namibian and Nigerian: A brilliant oval and a cabochon of fine Mandarin color]

As with all garnets, there are essentially no simulants or enhancements in the market to worry about and they are relatively hardy gems for jewelry use. Little precaution needs to be exerted in setting and wearing these gems.

[Spessartites in jewelry showing a range of hue, tone and saturation-- no worries here, all jewelry uses are OK, including rings]

Forty years ago, John Sinkankas wrote that the closer the Spessartites get to the ideal light orange color, the more likely they are to have inclusions.  This little perversity of nature holds true today, even with the recent discoveries in Namibia and Nigeria.  If it is not possible to remove the inclusions during the cutting, faceters try to orient the stones so that the inclusions are not directly below the table facet. It is common to find liquid filled inclusions, two-phase (liquid and gas) inclusions, and negative crystals in the Spessartites. Spessartite polishes easily and is a joy to cut because the facetor can be assured of a bright, scintillating finished gem.

[You can't get much more scintillating that this, Image courtesy of Barry Bridgestock]


Value Considerations

As with most non-diamond gemstones, color is everything when it comes to setting price. In the case of Spessartites, purity of color be it red-orange or orange is the hallmark of quality. Lesser prices will be awarded to gems with more brown in their hue. As with many gems, larger pieces command a higher per carat price than smaller stones, and clarity is always an issue. The beauty of the cut is a secondary factor modifying price.


Gemological Properties:

Makeup: Manganese aluminum silicate

Crystal System: cubic

RI: 1.79 - 1.81

Density: 4.1 - 4.2

Dispersion: .027

Polish Luster: vitreous to subadamantine

Cleavage: none

Fluoresence: inert


Stones Currently Available:

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Go to: Homepage -- what's new at ACS -- monthly specials and discounts -- "buried treasures" -- BWS/FS jewelry designs -- gem topic of the month -- gem topic archive -- birthstones -- ask Barbara -- key to all the codes used on the ACS site -- definitions of terms used on the ACS site -- how to order -- about ACS -- setting these gems -- free gemology course