While gemstone inclusions are generally viewed in a negative light because they represent imperfections, in certain cases the presence of "telltale" inclusions will have the opposite effect. Sometimes they turn out to be "perfect imperfections" — the type John Legend sang about in his 2013 hit, "All of Me" — and significantly increase a stone's value.
This is the case with the vivid green demantoid garnet, the rarest and most valuable variety of January’s birthstone.
First discovered in Russia’s Ural Mountains in 1851, the green gem was a favorite of designer Carl Fabergé, who incorporated demantoid into the famous jeweled eggs and other fanciful jewelry he created for the Russian Imperial family.
Demantoid garnet is currently mined in Namibia, Iran, Pakistan, Italy, Madagascar and Canada, but the Russian demantoid garnet continues to set the standard by which all the others are judged.
The good news is that jewelry connoisseurs can easily tell if their demantoid garnet was sourced in Russia due to distinctive byssolite “horsetail” inclusions that seem to spray out from the center of the stone.
A beautiful, well-formed inclusion can increase the value of the gemstone considerably, noted the International Colored Gemstone Association.
The gem in the first image, above, was sourced in Namibia, while the included gem in the second image originated in Russia's Ural Mountains.
Demantoid is derived from the Dutch word for diamond, “demant.” The stone owes its impressive diamond-like brilliance to two main factors: A high refractive index and a high dispersion (its ability to separate light into the spectrum of colors). Demantoid, in fact, boasts the highest dispersion rating of all gemstones, including diamond.
Fine-quality demantoid garnets are rarely found in sizes larger than 2 carats. The Namibian 3-carat gem, above, is part of the Smithsonian Gem and Mineral Collection and was purchased with funds from the Tiffany & Co. Foundation in 2014.
Ironically, George F. Kunz, who was Tiffany and Co.’s vice president of gemology from 1879 until his death in 1932, was a big fan of demantoid garnets and reportedly purchased all the rough material he could get his hands on.
African-origin demantoid tends to be yellowish-green, olive green or brownish, due to higher concentrations of iron. Russian demantoid, on the other hand, owes its color to chromium and tends to be vivid green.
Other garnet varieties used for jewelry include pyrope, almandine, andradite, grossularite, hessonite, rhodolite, tsavorite, spessartine and uvarovite.
Credits: Photo of Namibian demantoid garnet by Greg Polley/Smithsonian. Photo of Russian demantoid garnet with byssolite inclusions by Dr Anatoly, CC BY 4.0, via Wikimedia Commons.
