Sapphire is a gemstone variety of the mineral corundum, an aluminium oxide Al2O3, when in any color other than red or dark pink, in which case the gem would instead be called 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 sapphires are also called Padparadscha.
Sapphires are commonly worn as jewelery. Sapphires can be found naturally, by searching through certain sediments or rock formations, or they can be manufactured for industrial or decorative purposes in large crystal boules. Because of the remarkable hardness of sapphires and of aluminum oxide in general, sapphires are used in some non-ornamental applications, including infrared optical components, in scientific instruments, small high-durability windows also used in scientific instruments, wristwatch crystals, and very thin electronic wafers, which are used as the insulating substrates of very special-purpose solid-state electronics.
A Star Sapphire is a type of sapphire that exhibits a star-like phenomenon known as asterism. Star sapphires contain intersecting needle-like inclusions often the mineral rutile a mineral composed primarily of titanium dioxide that cause the appearance of a six-rayed star shaped pattern when viewed with a single overhead light source.