Sapphire (Greek: σάπφειρος; sappheiros, 'blue stone',[2] itself derived from Sanskrit "ShaniPriya" which probably referred instead at the time to lapis lazuli) is a typically blue gemstone variety of the mineral corundum, an aluminium oxide (α-Al2O3). Trace amounts of elements such as iron, titanium, chromium, copper, or magnesium can give corundum respectively blue, yellow, purple, orange, or green color. Chromium impurities in corundum yield pink or red tint, the latter being called ruby.

Commonly, sapphires are worn in jewelry. Sapphires may be found naturally, by searching through certain sediments (due to their resistance to being eroded compared to softer stones) or rock formations. They also may be manufactured for industrial or decorative purposes in large crystal boules. Because of the remarkable hardness of sapphires – 9 on the Mohs scale (the third hardest mineral, after diamond at 10 and moissanite at 9.5) – and of aluminium oxide in general, sapphires are used in some non-ornamental applications, including infrared optical components, such as in scientific instruments; high-durability windows; wristwatch crystals and movement bearings; and very thin electronic wafers, which are used as the insulating substrates of very special-purpose solid-state electronics (especially integrated circuits and GaN-based LEDs).

The sapphire is one of the three gem-varieties of corundum, the other two being ruby (defined as corundum in a shade of red) and padparadscha (a pinkish orange variety). Although blue is their most well-known color, sapphires may also be colorless and they are found in many colors including shades of gray and black.

The cost of natural sapphires varies depending on their color, clarity, size, cut, and overall quality – as well as their geographic origin. Significant sapphire deposits are found in Eastern Australia, Thailand, Sri Lanka, China (Shandong), Madagascar, East Africa, and in North America in a few locations, mostly in Montana.[3] Sapphire and rubies are often found in the same geographic environment, but one of the gems is usually more abundant in any of the sites.