The Blackfoot people have known about iridescent ammonite fossils for hundreds of years. The gem layer is transparent to translucent.Ī thin layer of iridescent color, often with a fractured appearance, on a base of siderite or shaleĪragonite, usually on a base of siderite or shale Red and green are the most common colors. Iridescent colors that can traverse the entire spectrum - red, orange, yellow, green, blue, indigo and violet. The ammonite fossils within these concretions sometimes have an outer shell layer composed of gem-quality Ammolite. Many of them served as a nucleus for the formation of siderite concretions which are now found in the Bearpaw Formation. When the ammonites died, their shells fell to the bottom of the seaway and were covered with sediment. The ammonites in the seaway grew to a diameter of up to one meter - but most were about 1/4 to 1/2 that size. Ammonites (the source organisms for Ammolite) are an extinct group of marine invertebrates that possessed a tightly coiled shell similar to the modern Nautilus. The Western Interior Seaway contained many forms of life, including bony fish, shellfish, sharks, sea turtles, and ammonites. The Bearpaw is composed primarily of marine shale but contains some thin sandstones and layers of volcanic ash. These sediments accumulated and eventually formed a rock unit known as the Bearpaw Formation. Rains falling on the eastern flank of the young Rocky Mountains washed sediments into the seaway. It connected what is now the Gulf of Mexico to the Arctic Ocean. The area on the east side of the mountains was covered by a broad body of water known as the Western Interior Seaway. The story of Ammolite begins about 70 to 75 million years ago when forces within the Earth were building the Rocky Mountains in what is now northwestern North America. Many stones are impregnated with epoxy for stability. Some Ammolite is made into doublets, which only requires adding a backing or transparent cover as needed. Black shale or another material can be used for the backing. These are made by backing the fragile iridescent material with a thin slab for stability and topping it with a transparent cover for protection.Ĭlear quartz or spinel can be used for the transparent cover. Most Ammolite is used to produce triplets. Exceptional pieces can be cut into gems without stabilization. The color-producing shell layer of Ammolite is usually very thin (often less than one millimeter) and attached to a dark gray to brown base of shale or siderite. Iridescent ammonite fossil: An ammonite fossil with iridescent shell material (Ammolite) mined from the Bearpaw Formation of Alberta, Canada and expertly prepared for display as a fossil specimen. Photo used here under a GNU Free Documentation License. The jewelry and Ammolite gemstones were produced by Korite International. Ammolite jewelry: Ammolite triplet cabochons used in two pendants and a pair of earrings, all with diamond accents.
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