The Star of India is a 563.35-carat (112.67 g) star sapphire, one of the largest such gems in the world. It is almost flawless and is unusual in that it has stars on both sides of the stone. The greyish-blue gem was mined in Sri Lanka and is housed in the American Museum of Natural History in New York City.

The milky quality of the stone is caused by the traces of the mineral rutile, which is also responsible for the star effect, known as asterism. The tiny fibers of the mineral, aligned in a three-fold pattern within the gem, reflect incoming light into the star pattern.

A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli and opal) and occasionally organic materials that are not minerals (such as amber, jet, and pearl) are also used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other physical properties that have aesthetic value. Rarity and notoriety are other characteristics that lend value to gemstones.

Apart from jewelry, from earliest antiquity engraved gems and hardstone carvings, such as cups, were major luxury art forms. A gem maker is called a lapidarist or gemcutter; a diamond cutter is called a diamantaire.