(Rev. 4:3, Revised King James Version, “sardius;” Hebrew: 'odhem; LXX, Greek: sardion, from a root meaning “red”)
a gem of a blood-red color
It was called “sardius” because it was obtained from Sardis in Lydia. It is enumerated among the precious stones in the high priest's breastplate (Exodus 28:17; 39:10).
It is our red carnelian.