GLASS
Heb. «z’kûkîth» (Jb. 28:17; in the Reina-Valera it is translated «diamond»; other versions translate «crystal») and from Gk. “hyalos” and its adjective (Rev. 4:6; 15:2; 21:18, 21).
It is probably real glass; It was already known by the Greeks in the time of Herodotus, and by the ancient Egyptians.