Sapphire (Greek: sappheiros) refers to gem varieties of the mineral corundum, an aluminium oxide (α-Al2O3), when it is a color other than red, in which case the gem would instead be a ruby. Trace amounts of other elements such as iron, titanium, or chromium can give corundum blue, yellow, pink, purple, orange, or greenish color. Pink-orange corundum are also sapphires, but are instead called padparadscha.
Because it is a gemstone, sapphire is commonly worn as jewelry. 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 wafers for the deposition of semiconductors.
Sapphire is one of the two gem varieties of corundum, the other being the red ruby. Although blue is the most well known hue, sapphire is any color of corundum except red. Sapphire may also be colorless, and it also occurs in the non-spectral shades gray and black.