Concise Bible Dictionary:
To what precious stone this word refers is not definitely known. It is mentioned as a symbol of preciousness: as “the price of wisdom is above rubies”; the value of a virtuous woman is far above rubies (Job 28:18; Prov. 3:15; Prov. 8:11; Prov. 20:15; Prov. 31:10). In Lamentations 4:7, where the Nazarites are said to be “more ruddy in body than rubies,” some translate “corals,” though the Hebrew is the same. Bochart judges “pearls” to be intended.