fibrolite, Sri Lanka, gems

Brown-black sillimanite cat's-eyesfrom Sri Lanka present an unusually sharp band, which would make them extraordinary gems wereit not for therather un-attractive body color of the stones. A study of six of these stones found that they contain 0.5 wt.% iron oxide.Theprincipal inclusionmineralisilmenite, which occurs in elongated, submicroscopically thin lamellae. Complex thicker lamellae consist of hercy-nite spinel grown together with a member of the pyroxene group. Thesethickerinclusions werenot foundin all of the specimens investigated.