Ammolite is the gems version of the fossil shell of the ammonite, a snail like shellfish, relative of the squid, which lived in the prehistoric oceans before 66 million years ago.
The wild rainbow colors come from the alternating layers of the shells nacre made from calcite and aragonite and not from opal. Gem grade ammolite is only found in the Bearpaw oil shale fields of southwestern Alberta, Canada.
The native people of the area called it "Iniskim" or Buffalo stone and used it as a talisman.
Ammolite is soft so it is often covered with a protective layer of quartz, glass or resin. First cut into gems into the 60's and in the 1980's recognized as a gemstone.