Shaligram
fossilized shell, typically in the form of spherical, black-coloured Ammonoid fossils of the Devonian-Cretaceous period, used in Vaishnava Hinduism as aniconic representations of Vishnu, usually collected from river-beds or banks
A shaligram, or shaligrama shila, is a fossilized stone or ammonite collected from the riverbed or banks of the Kali Gandaki, a tributary of the Gandaki River in Nepal. They are associated with Vishnu.