Iridescent ammonite (Placenticeras sp.) Shell,... Lot 12

Iridescent ammonite (Placenticeras sp.) Shell, ca. 83.5 million years old, Canada Ammonite mineralized into iridescent aragonite 36x30x4.5 cm Provenance: market (Italy) Conservation status. Surface area: 80%. Conservation status. Support: 80% (gaps, recomposed parts; consolidation by special resins and UV treatment) Extremely rare specimen. The fossil dates to the Upper Cretaceous, Campanian stage. This special mineralization occurs due to the numerous layers of volcanic ash (bentonite) found only in the Bearpaw Formation stratification in southern Alberta, Canada near the St. Mary River, where the fossil was excavated. In 1981 the World Jewellery Confederation (CIBJO) and the Gemmological Institute of America gave ammonites thus mineralized-known as ammolites-the status of gemstones. In fact, weight is measured in carats, as with diamonds, but ammolites are much rarer: in fact, in one ton of sedimentary material removed, an average of 0.6 kt of ammolite is found compared to 1.5 kt of diamond. The distinctive iridescent colors given off by this shell are due to the refraction of light on the different layers of the aragonite shell. Each color represents a different layer by which light originates an almost complete spectrum of the visible. Rare even in museum settings, this mineral fossil is preserved in an exceptional specimen with blue refraction at the Museo Mineralogico Campano.