HYACINTH or jacinth (q.v.) is a gem variety of the mineral zircon (zirconium silicate). It is transparent and generally red in color, but may be orange or brownish. The term prob. was used by ancient writers to refer to a blue material, such as blue corundum (sapphire in the gem variety) or turquoise (cf. Rev 21:20 NEB). See Jacinth.