Ammonite – click for larger image

Ammolite is both fossil and gemstone. It comes from the aragonite mother-of-pearl surrounding ammonites – jokingly called “grandmother-pearl”. Many ammonites still exhibit an iridescent sheen to them, however the ones from mines in southern Alberta exhibit a rainbow spectrum of gem-quality colors. Aragonite in life is an unstable organic crystal form of carbonate, and generally when a shell fossilizes, as it’s already a mineral, simply reverts to a more stable form of calcite. With Ammolite, the aragonite layers haven’t reverted – and the more layers there are, the more colors are refracted.

Ammolite grades

It was given gem status in 1981 by the World Jewelry Confederation. It is one of three organic gemstones – the other two being amber and pearls. If used in jewelry, because of the soft nature of the stone (only a 3.5-4 on the Mohs scale), it should only be set in earrings or pendants – not rings.

http://www.canadafossils.com/canadianammonites.php

http://en.wikipedia.org/wiki/Ammolite

http://www.ammolite.com/