Here's why it's considered the second hardest:
* Diamond is the hardest. It's known for its incredible resistance to scratching and abrasion.
* Corundum follows closely behind. It's used in many industrial applications, including sandpaper, grinding wheels, and watch crystals due to its durability.
Fun Fact: Ruby and Sapphire are varieties of corundum! The difference in color is due to trace impurities.
