jacinth

n. hyacinth, bulbous plant bearing reddish blue or deep purple flowers (native to the Mediterranean); reddish gemstone (Mineralogy)

Jacinth is a red transparent variety of zircon used as a gemstone. Jacinth is also 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 (Hebrew leshem) mentioned in Exodus 28:19 as the first stone of the third row in the high priest's breast-plate, the Hoshen. In Revelation 9:17 the word is simply descriptive of colour.
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Noun
1. a red transparent variety of zircon used as a gemstone
(synonym) hyacinth
(hypernym) zircon, zirconium silicate

(n.)
See Hyacinth.
  

a precious stone, forming one of the foundations of the walls of the new Jerusalem. (Revelation 21:20) Called hyacinth in the Revised Version. This is simply a different English rendering of the same Greek original. It is probably identical with the lighure of (Exodus 28:19) The Jacinth or hyacinth is a red variety of zircon, which is found in square prisms of a white, gray, red, reddish-brown, yellow or pale-green color. The expression in (Revelation 9:17) "of jacinth," is descriptive simply of a dark-purple color.