Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide (α-Al₂O₃) with trace amounts of elements such as iron, titanium, cobalt, lead, chromium, vanadium, magnesium, boron, and silicon. The name sapphire is derived from the Latin word sapphirus, itself from the Greek word sappheiros (σάπφειρος), which referred to lapis lazuli. It is typically blue, but natural "fancy" sapphires also occur in yellow, purple, orange, and green colors; "parti sapphires" show two or more colors. Red corundum stones also occur, but are called rubies rather than sapphires. Pink-colored corundum may be classified either as ruby or sapphire depending on locale. Commonly, natural sapphires are cut and polished into gemstones and worn in jewelry. They also may be created synthetically in laboratories 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) – sapphires are also used in some non-ornamental applications, such as infrared optical components, high-durability windows, wristwatch crystals and movement bearings, and very thin electronic wafers, which are used as the insulating substrates of special-purpose solid-state electronics such as integrated circuits and GaN-based blue LEDs. Sapphire is the birthstone for September and the gem of the 45th anniversary. A sapphire jubilee occurs after 65 years.

नीलम एक रत्न श्रेणी का खनिज है। यह अल्यूमिनियम भस्म (ऑक्साइड) (Al₂O₃) है, जब यह लाल के सिवाय अन्य वर्ण का होता है। नीलम प्रकृति में भी मिलता है, एवं कृत्रिम भी बनाया जाता है। अपनी उल्लेखनीय सख्तता के कारण कई अनुप्रयोगों में प्रयुक्त होता है, जैसे अधोरक्त दृष्टि सम्बन्धी उपकरण, घडी़ के क्रिस्टल, अर्धचालकों की डिपोसीशन हेतु जैसे कि।