Easton's Bible Dictionary (1897)/Carbuncle
Carbuncle : (Ex. 28:17; 39:10; Ezek. 28:13). Heb.@barkath; LXX. smaragdos; Vulgate, smaragdus; Revised Version, marg., "emerald." The Hebrew word is from a root meaning "to glitter," "lighten," "flash." When held up to the sun, this gem shines like a burning coal, a dark-red glowing coal, and hence is called "carbunculus", i.e., a little coal. It was one of the jewels in the first row of the high priest's breastplate. It has been conjectured by some that the garnet is meant. In Isa. 54:12 the Hebrew word is 'ekdah, used in the prophetic description of the glory and beauty of the mansions above. Next to the diamond it is the hardest and most costly of all precious stones.