Demantoid

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Demantoid.jpg
In 1868, during the reign of Tsar Alexander II of Russia - after whom the mineral alexandrite was named - a new garnet variety was discovered in the Ural mountains. This andradite garnet which is usually bright yellowish-green is one of the highest priced gemstones one can find, especially when it has the rare and intense grass green color which rivals emerald. It has a very high brilliancy and has a high dispersion, which adds to the beauty of the hue. It has a relative high refractive index, reasonable hardness and a vitreous to adamantine luster.

The major deposits for demantoid are found in alluvial deposits in The Ural mountain range along the Bobravka River and more recently demantoid was discovered in Namibia. The superb color of the finest Russian material is the hue by which all demantoids are judged. Stones with typical and well formed horsetail inclusions are some of the most coveted gemstones. The famous jeweler Fabergé used demantoids in his jewelry and made it a popular gemstone. At the end of the 19th century there was a true 'demantoid fever'.

The name of this gem means "diamond like", most probably due to its dispersive powers which actually outrank diamond but are usually suppressed by its body color.


Gemological information for demantoid
Color Brownish and yellowish-green to grass green and black
Crystal Structure Cubic
Refractive Index ca. 1.89
Durability Very durable
Hardness 6.5-7
Family Garnet - Andradite Species
Similar stones Demantoid may be confused with Tsavorite Garnet, Peridot, Emerald, Diopside and Tourmaline
Treatments Demantoids can be heated to improve their color
Localities

<googlemap lat="31.353637" lon="11.953125" zoom="1" width="700" height="400" controls="small" icon="http://www.langantiques.com/university/images/f/ff/Markeryellow.png">

58.745407, 56.898193,
Demantoid Garnet Russia 4ct.jpg
1853 - Ural Mountains, Russia. Demantoid first found, identified as green andradite in 1864, named demantoid in 1878 after the dutch diamant due to its adamantine luster and high dispersion. The deposit seemed exhausted at one point but around 1999 production continued and fine stones were found in the years after that. Typical inclusion: the so-called horsetail which is composed of chrysotile fibres.

-21.493964, 17.512207, 1997 - Deposit discovered in central Namibia. These stones typically show a yellow to brown secondary hue. Horsetail inclusions are absent. Namibian demantoid garnets have a lower Cr3+ content than the Ural demantoids. -13.599274, 48.455200, 2009 - Madagascar. Demantoid was found here by fisherman in 2008. Once the news got out in april 2009 thousands of miners came to the area to try their luck. The stones found have brown and yellow undertones. 19.694314, -97.155533, Mun. de Las Minas, Veracruz, Mexico - The color tends to be more on the yellow side but produces a good color-shift. The stones that are produced in that area are rather small. 46.250238, 9.850917, Val Malenco, Italy. Usually rather small crystals and more on the yellowish green than their famous Russian counterparts. Gem quality stones over 0.30 ct are rare. 35.371135, 54.250488, Iran - The Iranian material hit the rough markets around 2003. The color is a nice green but the clarity and size made faceting the material problematic. </googlemap>

Demantoid care
Ultrasonic cleaning Not safe
Steam cleaning Not safe
Warm soapy water Safe
Chemical attact Not safe
Light sensitivity None
Heat sensitivity Not safe
Lang Antiques
Lang Antiques