Bible Dictionary · D
Diamond
(1.) A precious gem (Heb. 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 (Ex 28:18; Ex 39:11; R.V. marg., “sardonyx.”)
(2.) A precious stone (Heb. shamir’, a sharp point) mentioned in Jer 17:1. From its hardness it was used for cutting and perforating other minerals. It is rendered “adamant” (q.v.) in Ezek 3:9, Zech 7:12. It is the hardest and most valuable of precious stones.
From Easton’s Bible Dictionary (1897), by Matthew George Easton.