Oncolite

Oncolites may have either a porostromate or spongiostromate texture. Most oncolites are spongiostromate, having no recognisable cellular texture or microstructure. Porostromate oncolites are mostly unknown during the Precambrian; since the Eocene they have mostly been confined to freshwater environments.

Distribution

The appearance of recent or near-recent freshwater oncoids has been documented in two rivers in Bavaria: the Alz, whose source is the Chiemsee, and the Moosach, near Freising. Modern oncoids also grow in some springs in Atacama Desert in South America. In one particular case a system of oncoids have been observed interface between Salar de Antofalla and an adjacent wetland.