Gem News International Gems & Gemology, Summer 2015, Vol. 51, No. 2

Large Namibian Demantoid Garnet

A selection of demantoid from Namibia’s Green Dragon mine.
Figure 1. This selection of andradite garnet from Namibia’s Green Dragon mine includes an 11.63 ct demantoid round brilliant, an unusually large stone for this source. Photo by Robert Weldon/GIA, courtesy of Green Dragon mine.
At the GJX show, Stefan Reif (Tsuen Wan, N.T., Hong Kong), showed us an 11.63 ct round brilliant demantoid garnet. It was an exceptional stone of intense vibrant green with a touch of blue. According to Reif, the original rough weighed approximately 46 ct—about 9 grams—making the yield a little over 25%. This is an exceptionally large gem for Namibia’s Green Dragon mine, where the bulk of production is suitable for small calibrated gems.

Namibian demantoid was first discovered in the 1990s (Fall 1997 GNI, pp. 222–223). The current production came from an open-pit, hard rock mine with an annual production between 5,000 and 10,000 carats. According to Reif, the local geology includes marble, pegmatite, and rhyolite. The distribution of demantoid pockets within these rocks is irregular and difficult to predict. Beside the geological challenges, water is scarce, and temperature extremes range from freezing at night to baking desert heat in the daytime.

The Green Dragon mine is renowned for its production of well-proportioned rough. This material is suitable for cutting smaller gems into 2–3 mm sizes in a range of colors from slightly bluish green through “lemongrass” green to greenish yellows and reddish browns. These are used for precision-cut calibrated and melee-sized goods placed as accent stones in high-end jewelry. Most of the cutting is done in Thailand, and the yield is approximately 10% due to the desire for well-proportioned cut gems. Besides precision-cut demantoid and andradite garnet in calibrated sizes, Reif also cuts to higher tolerances for the watch industry, producing 3 × 2 mm tapered baguettes for watch bezels.

Even in these small sizes, well-cut gems display high luster and very distinct fire, making them an excellent visual alternative to diamond. Rough suitable for gems of 6.0 mm (about 1 ct) is much rarer, but material for larger gems does come up once in a while.

Duncan Pay is editor-in-chief of Gems & Gemology.