Iridescent Kosmoceras Jurassic Russian Ammonite

Name: Kosmoceras sp.

Phylum Mollusca; Class Cephalopoda; Subclass Ammonoidea; Order Ammonitida

Geological Time: Jurassic, Callovian Stage

Size: 178 mm diameter

Fossil Site: Ulyanovsk, Russia

This large, beautiful ammonite is Kosmoceras coming from near Ulyanovsk, Russia. It exhibites opal iridescence of different colors that change with angle of view, a consequence of light passing through the various layers of aragonite and conchiolin deposited by the ammonite in life. The lack of acidity in the depositional environment allowed them to be preserved as you see it here. Jewel-quality material such as this coming from Alberta, Canada is termed “Ammolite” in the trade, and typically commands a high price. This is a stunning example of an enherent beauty often seen when ammonites were preserved in just the right environment.

click ammonite picture to enlarge


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