Easton’s Bible Dictionary
Emerald: Heb. nophek (Exodus 28:18; 39:11); i.e., the "glowing stone", probably the carbuncle, a precious stone in the breastplate of the high priest. It is mentioned (Revelation 21:19) as one of the foundations of the New Jerusalem. The name given to this stone in the New Testament Greek is smaragdos, which means "live coal."