Fossil Friday #4 – Ammolite: Alberta’s Fossil Gemstone

Polished ammolite.  Photo credit: http://www.gemselect.com/other-info/rare-ammolite.php

If you think diamonds are the most beautiful of the gemstones, you have clearly never seen ammolite.  Ammolite is an iridescent, opal-like gem that comes in an amazing range of vibrant colours that cover the complete visible spectrum.  The only fossil that can be commercially mined and sold in Canada, ammolite is made from the shells of an octopod-like creature called an ammonite.

An ammonite shell made of ammolite.  Photo credit: http://www.canadianammolite.com/AmmoliteFacts.html

Ammonites are a type of cephalopod, the group that includes the smartest and largest of the invertebrates, such as octopods, squid, and cuttlefish.  While most cephalopods today have no external hard parts, for much of the Paleozoic and Mesozoic, shelled cephalopods were common, and could often reach sizes comparable, or greater than that of today’s giant squid.  Like modern cephalopods, ammonites were voracious predators, although they were often the prey of large marine reptiles, such as mosasaurs.  Along with ammolite, in Alberta, we often find ammonites that have teeth marks in their shells from marine vertebrate predators.

An ammonite with teeth marks from the Royal Tyrrell Museum.  Photo credit: https://www.flickr.com/photos/tyrrellmuseum/6883571350

Ammonites went extinct at the end of the Cretaceous, along with their predators, the large marine reptiles, and the dinosaurs.  Today, there are only two small genera of shelled cephalopods left in the oceans, including a delightful little creature called Nautilus.

Nautilus. Photo credit: http://www/zoo-rostock.de/de/tiere+park/unsere_tiere?tierwelten/darwineum/nautilus

Not all ammonites produce ammolitic shells, at least, not in a commercially productive sense.  Ammolite is mostly produced by a specific genus of ammonite, Placenticeras, from the Bearpaw Formation (Late Cretaceous) of Alberta and Saskatchewan.  The world’s only ammolite mine is near the city of Lethbridge in southern Alberta.  Most ammolite is mined in pieces, which are made into jewelry, but if an intact specimen is uncovered, it will likely be sold as is.  There is one absolutely stunning specimen on display at the Royal Tyrrell Museum in Drumheller.  Ammolite is a great reminder that Alberta has more to offer palaeontologists and fossil enthusiasts than just dinosaurs.

Ammolite specimen at the Royal Tyrrell Museum.  Photo credit: https://www.tonmo.com/threads/royal-tyrell-ammolite-ammonite.15768/

For more information about ammolite, please check out the following article by Mychaluk et al. (2001): http://freeshipping.www.canadianammolite.com/SP01.pdf#page=5

Any questions or comments?  Suggestions for future Fossil Friday posts?  Let me know by leaving me a comment, or visiting my contact page!

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