San Venanzo, Marsciano, Terni Province, Umbria, Italy

The San Venanzo carbonatite comprises the two maars and tuff rings of San Venanzo and Pian di Celle, and the small cone of Celli. The area consists of crystal and lapilli tufts with abundant melilitite bombs, and there are also two lava flows at Pian di Celle. Celli is a lapilli tuff cone, erosion of which has exposed a cylindrical conduit filled with tuffisite. The pyroclastic rocks of the volcano vary from phonolitic to melilititic amongst which are units with varying proportions of primary calcite. The last comprise layers that almost totally consist of very fine-grained calcite in which occur sparse glass fragments and melilitic lapilli. The lava flows consist of kalsilite-phlogopite-olivine leucite melilitite (venanzite). Volcanic activity at San Venanzo has been dated by 39Ar-40Ar at 265,000 years.

Ref.:
- Stoppa, F., and Woolley, A.R. (1997): The Italian carbonatites: field occurrence, petrology and regional significance. Mineralogy and Petrology 59, 43-67.