Smith's Bible Dictionary
Adamant. The translation of the Hebrew word, Shamir in Ezekiel 3:9 and Zechariah 7:12. In Jeremiah 17:1, it is translated "diamond." In these three passages, the word is the representative of some stone of excessive hardness, and is used metaphorically. It is very probable that by Shamir is intended emery, a variety of corundum, a mineral inferior, only to the diamond in hardness.
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Smith, William, Dr. Entry for 'Adamant'. Smith's Bible Dictionary. https://www.studylight.org/dictionaries/eng/sbd/a/adamant.html. 1901.