Smith's Bible Dictionary
Jacinth. 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.
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Smith, William, Dr. Entry for 'Jacinth'. Smith's Bible Dictionary. https://www.studylight.org/dictionaries/eng/sbd/j/jacinth.html. 1901.