Corundum
/kəˈrʌndəm/
Definition 1 of 1
Pro Tip 1/3Material Strength
Corundum is extremely hard, second only to diamonds, which suggests high durability in its context. 
Due to its hardness, corundum is used in watch faces.
Pro Tip 2/3Gemstone Color
Corundum forms rubies or sapphires depending on trace elements, indicating its versatility in jewelry. 
While shopping for jewelry, I learned that both rubies and sapphires are actually colored corundum.
Pro Tip 3/3Industrial Usage
Corundum's abrasive qualities mean it's often mentioned in mechanical or industrial contexts. 
They used a corundum-coated disk for cutting the steel.