corundum

n.[矿]刚玉,金刚砂

a hard crystalline form of aluminum oxide, typically blue in color and used as a gemstone and abrasive.

名词

1. Rubies and sapphires are both varieties of corundum.
红宝石和蓝宝石都是刚玉的变种。

2. Corundum is one of the hardest minerals known to man.
刚玉是已知的最硬的矿物之一。