Girvanella sp. Oncolite
Oncolite Girvanella sp. (algal balls) stromatolite like
size: 18 cm x 13,5 cm
one side is polished one side is natural...is a super piece ofr any Museum Exhibition
Preparator: Di Silvestro Gianpaolo
cit. https://www.accessscience.com: Oncolites are a genus of cyanobacteria. The extinct members of the genus Girvanella are characterized by flexuous, tubular filaments of uniform diameter, composed of thick, calcareous walls. The external diameters of these cyanobacteria (formerly referred to as blue-green algae) average between 10 and 30 micrometers (μm), although specimens less than 10 μm and up to about 100 μm have been identified as Girvanella. Filaments may occur free (unattached), but they usually occur in groups, twisted together to form nodules and encrusting masses on various objects. The genus is intergrown with encrusting foraminifers in some Paleozoic limestones.