Which gemstone is most commonly used as the standard for the hardest natural gem?
Quick Answer
Ruby and sapphire, both varieties of corundum, rate 9 on the Mohs scale and are among the hardest common gemstones after diamond.
The Full Story
Ruby and sapphire are the gemstone varieties of corundum, one of the hardest natural minerals used in jewelry. On the Mohs scale, corundum has a hardness of 9, making it second only to diamond among common gemstones. Their durability is one reason they have been prized for centuries in rings, watches, and other ornaments. The red color of ruby comes mainly from trace amounts of chromium, while other trace elements produce the many colors of sapphire. Because of their hardness, these gems resist scratching better than most other jewelry stones.
Key Facts
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