Superb Pyritized Cosmoceras Ammonite on Large Matrix

Description: A superb large example of an ammonite of the genus Cosmoceras of the Callovian Stage (161 m.y.a) deposits of Russia. This fine example has had one side of the shell removed to allow you to see the intricate detail of the interior. You can easily see the individual chambers which were successively occupied in a spiral pattern by the ammonite as it grew. The septa (divisions) between the chambers are evident as the fine line between them. The environment was anoxic, leading to formation of Iron Pyrite (Fool’s Gold), crystals of which line each chamber for a dramatic effect. There is a second, smaller (31 mm) example which has been attached in the center to allow you to see what the ammonite’s original appearance had been. It displays well upon this dark concretionary matrix with the fine sand layer affording a good contrast.