Bismuth is a chemical element with the symbol Bi and atomic number 83. It is a metal with a pinkish-silver color that can develop an iridescent, rainbow-like oxide coating when exposed to air. Bismuth is heavy, brittle, and has a low toxicity, which makes it useful in a variety of applications, including in cosmetics, pharmaceuticals, and alloys. In its natural form, bismuth can occur in crystals or as grains in ore deposits. Bismuth is also popular in mineral collections due to its striking crystal shapes and colorful surface patterns. It has a Mohs hardness of 2.25.