Ammolite is a rare and valuable opal-like organic gemstone found primarily along the eastern slopes of the Rocky Mountains of the United States and Canada. It is arguably the rarest gemstone on Earth, rivaling the rarity of such gemstones as alexandrite and red diamonds. It is made of the fossilized shells of ammonites, which in turn are composed primarily of aragonite, the same mineral that makes up nacreous pearls. It is one of several biogenic gemstones; others include amber and pearl. In 1981, ammolite was given official gemstone status by the World Jewellery Confederation, the same year commercial mining of ammolite began.
Ammolite is also known as aapoak (Kainah for "small, crawling stone"), gem ammonite, calcentine, and korite. The latter is a trade name given to the gemstone by the Alberta-based mining company Korite International, the first and largest commercial producer of ammolite.