What are Rubies and Sapphires chemically known as?

Rubies and sapphires are both varieties of the mineral corundum, which is chemically known as aluminium oxide. In their pure form, these crystals are colorless. The distinct colors are caused by trace amounts of impurities. For example, chromium creates the red color in rubies, while elements like iron and titanium produce the blue color in sapphires. Because they are the same mineral with the same chemical base, they share the same hardness and structure. Silicon dioxide refers to quartz, lead tetroxide is red lead, and boron nitride is a synthetic material. Therefore, aluminium oxide is the correct chemical identity.