Here's why:
* Hardness is a relative scale: The Mohs Hardness Scale measures a mineral's resistance to scratching. Diamonds are the hardest known natural mineral, with a score of 10. Everything else is ranked relative to diamonds.
* No "second place": While some gemstones are very close in hardness to diamond (like moissanite, with a score of 9.25), there's no definitive "second hardest" gemstone.
Instead of thinking about "second hardest," it's more helpful to look at the ranking of gemstones on the Mohs scale:
* Diamond: 10
* Moissanite: 9.25
* Corundum (Sapphire and Ruby): 9
* Topaz: 8
* Quartz (Amethyst, Citrine, etc.): 7
* Feldspar: 6
* Apatite: 5
* Fluorite: 4
* Calcite: 3
* Gypsum: 2
* Talc: 1
This scale helps you understand which gemstones are more resistant to scratches than others.
