From BiblePortal Wikipedia

Watson's Biblical & Theological Dictionary [1]

ברקת ,  Exodus 28:17;  Exodus 39:10;  Ezekiel 28:13; and ανθρεξ , Ecclesiastes 32:5; Tob_13:17; a very elegant and rare gem, known to the ancients by the name ανθραξ , or coal, because, when held up before the sun, it appears like a piece of bright burning charcoal: the name carbunculus has the same meaning. It was the third stone in the first row of the pectoral; and is mentioned among the glorious stones of which the new Jerusalem is figuratively said to be built. Bishop Lowth observes that the precious stones, mentioned   Isaiah 54:11-12 , and  Revelation 21:18 , seem to be general images to express beauty, magnificence, purity, strength, and solidity, agreeably to the ideas of the eastern nations; and to have never been intended to be strictly scrutinized, and minutely and particularly explained, as if they had some precise moral or spiritual meaning. Tobit, in his prophecy of the final restoration of Israel, Tob_12:16-17 , describes the new Jerusalem in the same oriental manner.

Webster's Dictionary [2]

(1): (n.) A beautiful gem of a deep red color (with a mixture of scarlet) called by the Greeks anthrax; found in the East Indies. When held up to the sun, it loses its deep tinge, and becomes of the color of burning coal. The name belongs for the most part to ruby sapphire, though it has been also given to red spinel and garnet.

(2): (n.) A charge or bearing supposed to represent the precious stone. It has eight scepters or staves radiating from a common center. Called also escarbuncle.

(3): (n.) A very painful acute local inflammation of the subcutaneous tissue, esp. of the trunk or back of the neck, characterized by brawny hardness of the affected parts, sloughing of the skin and deeper tissues, and marked constitutional depression. It differs from a boil in size, tendency to spread, and the absence of a central core, and is frequently fatal. It is also called anthrax.

Fausset's Bible Dictionary [3]

(in English "a little coal," "a bright red gem"): Eqedach , Boreqeth , the former in  Isaiah 54:12 from Qadach "to burn," the latter from Baraq "to flash." A brightly flashing stone. A smaragd (Septuagint) or corundum, of green glass color, transparent, and doubly refractive; the emerald ( Exodus 28:17); third stone in the first row m the high priest's breast-plate ( Ezekiel 28:13).

People's Dictionary of the Bible [4]

Carbuncle. One of the gems in the high priest's breast-plate,  Exodus 28:17;  Exodus 39:10; it is also mentioned in  Ezekiel 28:13. It must, from the derivation of the Hebrew word, have been a bright flashing gem. Some have supposed it the emerald. Carbuncle occurs again as the rendering of another term in  Isaiah 54:12. The original words here may mean "sparkling stones;" perhaps the Oriental garnet is intended.

Smith's Bible Dictionary [5]

Carbuncle. This word represents two Hebrew words. The first may be a general term to denote any Bright,Sparkling Gem ,  Isaiah 54:12; the second term,  Exodus 28:17;  Exodus 39:10;  Ezekiel 28:13, is supposed to be any smaragdus or Emerald.

American Tract Society Bible Dictionary [6]

A precious stone, like a large ruby or garnet, of a dark, deep red color, said to glitter even in the dark, and to sparkle more than the ruby. The word is put to represent two different Hebrew words, one of which,  Exodus 28:17;  Ezekiel 28:13 , is commonly thought to mean the emerald; and the other,  Isaiah 54:12 , may mean a brilliant species of ruby.

Morrish Bible Dictionary [7]

Two Hebrew words are so translated.

1. eqdach, a stone of a fiery sparkling nature.  Isaiah 54:12 .

2. bareqeth, a stone of a glittering brightness.  Exodus 28:17;  Exodus 39:10;  Ezekiel 28:13 .

Easton's Bible Dictionary [8]

 Exodus 28:17 39:10 Ezekiel 28:13 Isaiah 54:12 'Ekdah

Holman Bible Dictionary [9]

 Exodus 28:17 Ezekiel 28:13 Isaiah 54:12

Hastings' Dictionary of the Bible [10]

CARBUNCLE . See Jewels and Precious Stones.

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [11]

is the rendering in the Auth. Vers. of the following Hebrews and Gr. words: 1. אֶקְדָּח , Ekdach', only  Isaiah 54:12 (Sept. Κρύσταλλος , Vulg. [Lapis] Sculptus), some Sparkling gem (from קָדִח , to Inflame). 2. בָּרֶקֶת , Bare'Keth, only  Exodus 28:17;  Exodus 39:10, as the third in the first row of the high-priest's breastplate (Sept. Σμάραγδος , Vulg. Smaragdus, i.e. emerald); or בּ רקִת , Barekath', only  Ezekiel 28:13 (Sept. Ὀνύχιον , Vulg. Smaragdus). From the etymology ( בָּרִק , To Flash), we assume that a stone of a bright coruscant color is meant. Kalisch translates it Smaragd, or emerald, and says it is a sort of precious corundum of strong glass luster, a beautiful green color, with many degrees of shade, pellucid and doubly refractive. Pliny enumerates twelve species of emerald. They are not rare in Egypt (see Braun. De Vest. Sacerdott. p. 517 sq.). 3. ῎Ανθραξ , lit. a Coal of fire,  Tobit 13:17;  Sirach 32:5. 4. The carbuncle is thought by many to be denoted by the word נֹפֶךְ , No'Phek ("emerald,"  Exodus 28:18;  Exodus 39:11;  Ezekiel 27:16;  Ezekiel 28:13). (See Emerald). Under the name "carbuncle" are comprehended several brilliant red stones of the clay family which resemble a glowing coal, such as the ruby, the garnet, the spinel, but particularly the almandin, that is, the noble Oriental garnet, a transparent red stone with a violet shade and strong glass luster. Probably it is not so hard as the ruby, which, indeed, is the most beautiful and costly of the precious stones of red color, but, at the same time, so hard that engravings cannot easily be made in it (Rosenm Ü ller, Alterth. 4:1, 34). In the present state of our knowled e respecting the ancient Hebrew mineralogy, it is impossible to determine with precision what particular gem is denoted by either of these terms, although they all evidently were precious stones of a brilliant fiery hue. (See Gem).

Kitto's Popular Cyclopedia of Biblial Literature [12]

Car´buncle. There are two Hebrew words rendered by 'Carbuncle' in the Authorized Version. One of them, Nophech which occurs in ; ; , appears to have been a kind of ruby or garnet, perhaps the noble Oriental garnet, which is a transparent red stone, with a violet shade, and strong glossy luster. The other word is Ekdach which occurs in , where the gates of the new Jerusalem are described as being composed of it. It seems to denote some stone of a fiery luster, but the particular kind cannot well be determined.