From BiblePortal Wikipedia

Holman Bible Dictionary [1]

 Ezekiel 28:13  Revelation 4:3  Revelation 21:20

Webster's Dictionary [2]

(n.) A variety of chalcedony, of a clear, deep red, flesh red, or reddish white color. It is moderately hard, capable of a good polish, and often used for seals.

Hastings' Dictionary of the Bible [3]

Carnelian . See Agate under Jewels.