|Easton's Bible Dictionary|
Properly a flower of a reddish blue or deep purple (hyacinth), and hence a precious stone of that colour (Revelation 21:20). It has been supposed to designate the same stone as the ligure (Hebrews leshem) mentioned in Exodus 28:19 as the first stone of the third row in the high priest's breast-plate. In Revelation 9:17 the word is simply descriptive of colour.
Noah Webster's Dictionary
(n.) See Hyacinth.
Int. Standard Bible Encyclopedia
See HYACINTH; STONES, PRECIOUS.
Jacinth (4 Occurrences)
Revelation 9:17 And thus I saw the horses in the vision, and them that sat on them, having breastplates of fire, and of jacinth, and brimstone: and the heads of the horses were as the heads of lions; and out of their mouths issued fire and smoke and brimstone. (KJV DBY WBS YLT)
Revelation 21:20 the fifth, sardonyx; the sixth, sardius; the seventh, chrysolite; the eighth, beryl; the ninth, topaz; the tenth, chrysoprasus; the eleventh, jacinth; and the twelfth, amethyst. (WEB KJV WEY ASV BBE DBY WBS YLT NAS RSV NIV)
Exodus 28:19 and the third row a jacinth, an agate, and an amethyst; (WEB JPS ASV BBE NAS RSV NIV)
Exodus 39:12 and the third row, a jacinth, an agate, and an amethyst; (WEB JPS ASV BBE NAS RSV NIV)