Sapphire (Greek: σάπφειρος; sappheiros "blue stone") is a gemstone variety of the mineral corundum, an aluminium oxide (α-Al2O3), when it is a color other than red or dark pink, in which case the gem would instead be called a ruby, considered to be a different gemstone. 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. Pure chromium is the distinct impurity of rubies. However, a combination of e.g. chromium and titanium can give a sapphire of a color distinct from red.
Sapphires are commonly worn as jewellery. 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, such as 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 (most of which are integrated circuits).
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