Easton's Bible Dictionary (1897)
Heb. nophek (Ex. 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 (Rev. 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.”
Smith's Bible Dictionary (1863)
a precious stone of a rich green color, upon which its value chiefly depends. This gem was the first in the second row on the breastplate of the high priest. (Exodus 28:18; 39:11) It was imported to Tyre from Syria, (Ezekiel 27:16) was used as a seal or signet, Ecclus. 32:6, as an ornament of clothing and bedding, (Ezekiel 28:13; Judges 10:21) and is spoken of as one of the foundations of Jerusalem. (Revelation 21:19) Tob. 13:16. The rainbow
around the throne is compared to emerald in (Revelation 4:3)
Hastings' Dictionary of the Bible (1898) & Schaff's Bible Dictionary
EM'ERALD (perhaps the glowing), a very precious gem of a pure green color, to which it owes its chief value, as the deepest colors are the most esteemed. Ex 28:18; Eze 27:16; Eze 28:13. The emerald was anciently obtained from Egypt. There is little question that the original word should have been translated "carbuncle." This gem is "a garnet cut with a convex face." See Stones, Precious.