Adam Clarke on Job 28:19

The topaz of Ethiopia - The country called Cush, which we call Ethiopia, is supposed to be that which extends from the eastern coast of the Red Sea, and stretches towards Lower Egypt. Diodorus Siculus says that the topaz was found in great abundance, as his description intimates, in an island in the Red Sea called Ophiodes, or the isle of serpents, Hist. lib. iii., p. 121. His account is curious, but I greatly doubt its correctness; it seems too much in the form of a legend: yet the reader may consult the place. See also Clarke on Job 28:16 (note).