Demantoid Garnet

Demantoid is the collector's garnet. Its dispersion — the splitting of white light into spectral color — is higher than diamond's, so a well-cut stone throws fire no other green gem manages. The name is a nod to it.

It is rare, and rare in size especially: most demantoid is under a carat, and anything larger is a serious stone. Horsetail inclusions, the fine golden fibers found in some material, are prized here rather than penalized — a clean stone is not automatically the better one. Mohs 6.5 to 7, so a protected setting suits it.