What are Rubies and Sapphires chemically known as?

a) Silicon dioxide

b) Aluminium oxide

c) Lead tetroxide

d) Boron Nitride

Sapphire refers to gem varieties of the mineral corundum, an aluminium oxide (Al₂O₃) when it is color other than red. Sapphire can be found naturally or manufactured in large crystal boules. Because of its remarkable hardness sapphire is used in many applications, including infrared optical components, watch crystals, high durability windows and for the deposition of semiconductors, such as GaN nanorods. Sapphire includes any gemstone quality varieties of the mineral corundum except the fully saturated red variety, which is instead known as ruby, and the pinkish orange variety known as padparascha.