Name Meaning: From Amon (Egyptian God)
Geologic Era: Devonian through Cretaceous
Location Discovered: Madagascar
Estimated Range: Worldwide
Size: Up to 2 meters in diameter (most species much smaller)
Extinction Date: End of Cretaceous (K-T extinction)
All four of the ammonites pictured below were meant for the jewelry trade. The first two pictures show the exterior and interior of the same specimen. The last, reddish colored one is a true example of ammolite, or gem-quality fossilized ammonite.
Ammonites grew by adding to their shell as their soft bodies grew larger. This allowed for the full body to remain protected. Generally, the more sections the shell contains, the older the ammonite. Juvenile ammonites probably would have made up part of plankton, and would have stayed near the surface of the ocean. Only when they grew larger would they become bottom feeders. This feeding strategy meant that juveniles were not competing with the adults for food. However, it did put them at greater risk from filter feeding animals, which are very indiscriminate as to what they gulp down.
Ammonites probably engaged in a “spawn-and-die” reproductive strategy, with adults releasing gametes at the end of their lives and then dying. The offspring would then migrate to the surface. This strategy, however, might have been the ultimate demise of the ammonites. The last of these animal types died during the K-T extinction, which is thought to be linked to a meteor strike. Residual heat and radiation would have most affected the upper levels of the ocean, where the young ammonites were. If that was the case, entire generations of ammonites would have been wiped out quickly, making further breeding and reproduction impossible.
Gem quality ammolite can be found in a variety of places, but the finest specimens come from Madagascar and Canada. Ammolite is a very fragile mineral, and is easily damaged and fragmented in the mining process. Certain colors are prized above others, with blue and purple being the rarest. Our specimen, a pinkish-red, is not terribly rare or valuable, but is still pretty to look at. If it were further processed, it would probably have been made into a pendant or earrings. Ammolite is easily broken, and so is difficult to make into bracelets or rings (which tend to see a lot of movement and friction).
Since blue and purple ammolite is most prized, the mineral labradorite is sometimes put forward as gem ammolite. People experienced with gems can usually tell the difference, but a novice might be fooled. Labradorite has a different “flash” pattern than true ammolite, and that is the best way to tell the difference.
Life Restoration: By Nobu Tamura (http://spinops.blogspot.com) – Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=19460396