Demantoid was discovered in 1849 but named in 1855 by Dr. Nils Gustaf Nordenskjöld, the man also responsible for naming Alexandrite. The original source was in Russia's central Urals. The name was taken from the German word ‘demant’ meaning diamond-like, in reference to Demantoid's lustre, extreme scintillation and a fire (also dispersion, the splitting of light into its component colours) greater than in Diamonds.
History of Demantoid
Due to colour similarities, Demantoid was originally assumed to be Emerald and then mistakenly sold as Chrysolite. Although an important gemstone in high-end Victorian Jewellery, Demantoid’s greatest impact was in its homeland of Imperial Russia. Popular with the Tsar’s court jewellers in the late 19th to early 20th centuries, Demantoid was a favourite of the Russian goldsmith behind the golden eggs, Peter Carl Fabergé. Also coveted by George Frederick Kunz, chief gemologist for Tiffany & Co., who went to Russia with the purpose of purchasing as much Demantoid as possible.
Composition of Demantoid
Demantoid and the Grossular Garnet, Tsavorite are the two green gemstones of the Garnet family. Coming in a range of colours, including blues, chocolates, greens, oranges, pinks, purples, reds and yellows, Garnets are a group of minerals that have similar crystal structures, but vary in composition.
Properties of Demantoid
The colour spectrum of Demantoid ranges from bright forest green, green, grass green and carary yellow green. This colour comes from chromium and/or iron, just like Emerald. The more yellow the Demantoid, the more iron it has in its crystal structure.
An intense 'emerald-green,' is regarded as the ‘happy medium’ for Demantoid. Demantoid generally looks better in daylight and generally appears slightly more yellowish in incandescent light. The stellar 'diamond-esque' optical properties set it apart from Emerald, and contribute to its amazing brilliance. Demantoid has the highest fire of all the Garnets; its dispersion is 0.057, making it even higher than Diamond's (0.044). Due to its body colour, greater fire is often not as discernable as a Diamonds. There's definitely a trade-off between richness of body colour and visible fire, with lighter Demantoids displaying more fire than those darker.
Although classed as a Type II gemstone (some minor inclusions that may be eye-visible), the marketplace standard is eye-clean (no visible inclusions when the gem is examined six inches from the naked eye). Demantoid over half a carat usually isn't eye-clean, with the majority mined smaller than 1 carat. Gemstones one to two carats in size are extremely rare. European and African Demantoid are differentiated by 'horsetail' inclusions, radiating strands that appear similar to a horse's tail. Namibian and Madagascan Demantoid do not have true horsetails. While it is usually available as oval, round brilliant or cushion cuts, other shapes are available, sometimes at a premium.
Source of Demantoid
Today mined in Iran, Italy, Madagascar, Mozambique and Namibia, the marketplace standard is still the pure, intense greens of Russian Demantoid. New Russian Demantoid deposits were discovered in the 90s including Karkodino, Kamchatka, Chukotka, but poor weather conditions and rough terrain make the mining season last only 3 months. Namibian Demantoid doesn't fair much better, with most of the claims lying in the extremely harsh and arid Namib Desert. Madagascan Demantoid's rarity is once again accentuated by difficult mining terrain; the deposit is located in the boggy mangroves of a shore line.