Adamant
ADAMANT. The Hebrew word shāmîr, in NIV translated “flint” (Jer.17.1) and “hardest stone” (Ezek.3.9), is spelled identically with the word translated “brier” in Isa.5.6, but is not now thought to be the same word. See also Minerals, Precious Stones.
ADAMANT means invincible, or a thing (mineral or metal) which is impenetrably hard (Ezek 3:9). Present day use (uncommon) is as a synonym for diamond (q.v.) (cf. KJV and NEB Jer 17:1), although up to the 17th cent. there was a confusion of ideas between diamond (or other hard gems) and loadstone or magnetite, the magnetic iron oxide (ad-amantem—having an attraction for). The term was applied by Theophrastus to the hardest crystalline gem then known, the emery stone of Naxos, Greece, emery being a massive form of corundum (aluminium oxide) mixed with iron oxides, which is used for polishing hard surfaces. In Lat. it was used, poetically, for the hardest iron or steel, or anything hard or indestructible. Pliny used it to refer to a transparent crystalline gem, prob. corundum (white sapphire), which among natural minerals is next in hardness to diamond.