Demantoid

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Demantoid.jpg

At the end of the reign of Nicholas I, Emperor of Russia, and the beginning of the reign of Tsar Alexander II - after whom the mineral alexandrite was named - a new garnet variety was discovered in the Ural mountains. Circa 1853, in the settlement of Elizaventinskoye, a group of children found some pretty green pebbles along the Bobrovka River. The stones were identified at the time as chrysolite or olivine, otherwise known as peridot. A visiting Finnish mineralogist, Nils von Nordensheld, declared that the stones were actually a new mineral (definitely not chrysolite.) He spoke before the St. Petersburg Mineralogical Society in February of 1864 pronouncing the new mineral to be an andradite variety of garnet with a chromium component. The gem's high refractive index and dispersive powers, which actually outrank diamond but are usually suppressed by its bodycolor, soon earned it the name demantoid (diamond-like).

Soon demantoids were being incorporated in some of the finest jewelry ever created. The famous court jeweler Fabergé used demantoids in his jewelry and made it a very popular gemstone. At the end of the 19th century there was a true 'demantoid fever' infecting all of Europe. The Edwardian and Belle Epoque jewelery periods were literally punctuated by demantoid garnets. Unfortunately, Russian gem production was effectively halted by the Bolshevik Revolution in 1917. Personal adornment was no longer a priority and the Urals began to produce more industrial products, especially at the onset of World War II when they primarily produced war machinery.

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.

Two major districts in Russia within the Central Ural Mountains have historically produced demantoid. The Nizhniy Tagil district, near Elizavetinskoye, contains placer deposits along the Bobravka River and the primary deposit at the head of the Bobrovka River, which is also the source of the placer deposits. The Sissertsk district at Kladovka and Korkodin there are a primary deposits. In addition, there are five river placers in the region. There are also some new discoveries in the Arctic Urals that have not been fully explored and examined. Mining in these areas has been sporadic and often only as a by-product of platinum and gold mining. Since 1915 most of the demantoid has been minded by private, illegal miners or by locals picking over the tailings piles. Namibia has also been producing some demantoid, but not with the same vibrant color as the Ural deposits.

Russian Demantoid Garnet with Horsetail Inclusion. Photo Courtesy of Constantin Wild.


Demantoid gets its desirable green color from the inclusion of chromium in to the andradite composition. The color rages from yellowish or brownish green to an incredible, bright yellowish green. 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, an inclusion unique to demantoid and found in most Russian specimens, are some of the most coveted gemstones. Most demantoids are less than 1 carat, but there are rare, larger exceptions to this rule. Tsavorite (a green form of grossular garnet) gets its color from vanadium and its finest specimens are sometimes confused with/sold as demantoid.


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

Sources

Phillips, Wm. Revell and Talantsev, Anatoly S. Russian Demantoid, Czar of the Garnet Family. Gems & Gemology; Summer 1996.

Lang Antiques
Lang Antiques