Fausset's Bible Dictionary
One of the hyaline corundums; deep blue, hard, brilliant, and costly. Representing the hue of the divine throne. On the high-priest's breast-plate (Exodus 28:18); some think the lapis lazuli is meant (Exodus 24:10). Ezekiel 1:26; Ezekiel 10:1; Job 28:6; Job 28:16; Song of Solomon 5:14, sapphire, sparkling in the girdle round Him; Isaiah 54:11; Lamentations 4:7, "their polishing was of sapphire," they were like beautifully cut and polished sapphires. The sapphires represent the blue veins of a beautiful person (Ezekiel 28:13). The best sapphires came from Persia. Our sapphire is the azure or indigo blue, crystalline corundum; but the Latin and Greek sapphire was "refulgent with spots of gold, azure, never transparent, not suited for engraving when intersected with hard crystalline particles" (Pliny, H. N. 37:9); i.e. the lapis lazuli. The Hebrew lapis lazuli is transparent and suited for engraving; probably our sapphire.
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Fausset, Andrew R. Entry for 'Sapphire'. Fausset's Bible Dictionary. https://www.studylight.org/dictionaries/eng/fbd/s/sapphire.html. 1949.