The distinctive features of demantoid are the characteristic inclusions of yellow byssolite (asbestos) fibers with radiating arrangements known as 'horsetails'. Although the horsetails are diagnostic for demantoid, they are not required for a stone to be identified as a demantoid. The identification of demantoid is based on the chemistry and refractive index of the stone. Many stones do not have horsetails at all.
Apparently, only the Russian demantoids possess the horsetail inclusions. Namibian stones are not known to ever have horsetails. The Pakistani stones may have occasional horsetails or possibly single fibers of byssolite but this has not been confirmed. If the horsetail-byssolite inclusions are present in the Pakistani stones, they are not clearly defined and very difficult to distinguish from the other inclusions.
Although, the Russian stones with horsetails seem to be worth much more than the demantoids from other localities, we also value demantoids according to their color and clarity. Demantoid has a very high refractive index (even higher than diamond) and will be remarkably bright and beautiful if cut correctly. If the color, cut, and clarity are good but the stone does not have horsetails, it is still a valuable stone.
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