Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO4(F,OH)2. It is used as a gemstone in jewelry and other adornments. Common topaz in its natural state is colorless, though trace element impurities can make it pale blue or golden brown to yellow orange. Topaz is often treated with heat or radiation to make it a deep blue, reddish-orange, pale green, pink, or purple.

Topaz in its natural state is colorless, often with a greyish cast. It also occurs as a golden brown to yellow which makes it sometimes confused with citrine, a less valuable gemstone. The specific gravity of all shades of topaz, however, means that it is considerably heavier than citrine (about 25% per volume) and this difference in weight can be used to distinguish two stones of equal volume. Also, if the volume of a given stone can be determined, its weight if topaz can be established and then checked with a sensitive scale. Likewise, glass stones are also much lighter than equally sized topaz.