ChristianAnswers.Net WebBible Encyclopedia
A precious gem (Hebrew: yahalom', in allusion to its hardness), otherwise unknown, the sixth, i.e., the third in the second row, in the breastplate of the high priest, with the name of Naphtali engraven on it (Exodus 28:18; 39:11; Revised King James Version marginal note, “sardonyx.”)
A precious stone (Hebrew: shamir', a sharp point) mentioned in Jeremiah 17:1. From its hardness, it was used for cutting and perforating other minerals. It is rendered “adamant” in Ezek. 3:9, Zechariah 7:12. It is the hardest and most valuable of precious stones.