Ammonite fossil "Placenticeras costatum - Lot 169

Ammonite fossil "Placenticeras costatum preserved in a sparkling ammolite gemstone Canada, Alberta St. Mary River Valley Polymorph of CaCO3 aragonite with minor amounts of pyrite from the Upper Cretaceous Bearpaw Formation 71 million years ago Height: 36 cm Width: 44 cm Weight: 6.5 kg Placenticeras was a fast-swimming carnivorous cephalopod, the taxonomic class that includes today's octopus, nautilus and squid. Like a submarine, these ammonites used gas- and fluid-filled chambers to regulate their position in the water column. The animals themselves lived only in the outermost compartment, using their tubular siphon to connect its chambers along the ventral surface of their shells. While dinosaurs ruled the earth during the Upper Cretaceous, Placenticeras Placenticeras ammonites could be found in the world's oceans. However, the vast majority of this species made their home in the Western Interior Seaway, an ocean that bisects North America from the Arctic Circle to what is now the Gulf of Mexico. Gulf of Mexico. Under ideal preservation conditions, a recently deceased ammonite would sink and filled with sediment. Over time, its muddy grave eventually mineralized mineralized into shale, and it was these ancient shale deposits of the Canadian Rockies that the world's largest and only gem-quality ammolite deposits (a semi-precious stone recognized worldwide as such). Along with amber and pearl, ammolite is one of the world's few biogenic substances. Resembling opal, it is found exclusively in ammonite shells that have undergone the fossilization process known as permineralization. The quality of gem ammolite is determined by a number of factors, the first and most obvious being its number of primary colors - reds and greens are fairly common, while blues and purples appear much more rarely. The amplitude of ammolite's chromatic change, graded by the way its colors change hue and intensity as they diffract light at different angles, also has an impact on its quality and value, with the finest specimens displaying broad, uninterrupted bands of brilliant, rainbow colors. rainbow colors. On all these indicators, this ammolite specimen ranks favorably. As a stunning example of an ammonite from Canada's world-renowned Bearpaw Formation, the Placenticeras meeki offered here is a shimmering example of one of the most beautiful ammolite fossils ever put on the market. It is, in my own expert words, an exceptionally large, iridescent ammonite with superb ammolite mineralization. This exceptional specimen features superb ammolite mineralization, a precious gem recognized as such by jewellers, on both sides, one with shimmering, iridescent reds, golds and greens, the other with a rainbow of blues, greens, yellows, purples, dark browns and tan. The colors change hue and intensity as they diffract light from different angles, turning the room into a natural work of art in the spirit of the Surrealists.