King James Bible Dictionary

(Exodus 28:17; 39:10; Ezekiel 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 Isaiah 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.

A precious stone
Isaiah 54:12; Ezekiel 28:13

One of the precious stones set in breastplate
Exodus 28:17; Exodus 39:10

This word represents two Hebrew words. The first may he a general term to denote any bright,sparkling gem , (Isaiah 54:12) the second, (Exodus 28:17; 39:10; Ezekiel 28:13) is supposed to be and smaragdus or emerald.

CARBUNCLED, adjective Set with carbuncles; spotted.