יהלם . Exodus 28:18; Exodus 29:11; Ezekiel 28:13 . This has from remote antiquity been considered as the most valuable, or, more properly, the most costly substance in nature. The reason of the high estimation in which it was held by the ancients was its rarity and its extreme hardness and brilliancy. It filled the sixth place in the high priest's breastplate, and on it was engraven the name of Naphtali.