oriental emerald

:  a green corundum used as a gem In a way this is odd, since, unlike rubies and sapphires, today's commercial emeralds are a green-tinted form not of corundum but of beryl, a different mineral entirely. Yet there is a green corundum, too, known commercially as “Oriental emerald,” which was not distinguished from green beryl in antiquity. — ‘Philologos’, The Jewish Daily Forward, 14 May 2004