Analysis of moonmilk nanofibers in the etruscan tombs of Tarquinia

The moonmilk is a secondary calcite deposit (speleothem) formed by nanofibers of calcite and commonly found in karst caves. While its biogenic origin is widely accepted, the mechanism of calcite nanofibers production remains unclear. Crystallization and formation mechanism of calcium carbonate nanostructures are of high interest in different fields, such as geomicrobiology (rock-microbes interactions), astrobiology (biosignatures), medicine (antibiotics producing bacteria), nanotechnology (calcium carbonate nanofibers) and recently, archeology. The discovery of the moonmilk in the hypogeal tombs of the ancient necropolis of Tarquinia (Italy), provides a unique opportunity to compare moonmilk crystal shapes that originated from two type of rocks, Macco (a calcarenite) and Sabbione (a hybrid sandstone). We analyzed, through a SEM analysis, moonmilk samples from twelve tombs in the necropolis area and found that rocks provide an ideal environment for the formation of the nanofibers; the Sabbione promoted the growth of a finer and thinner carbonate nanostructures, probably due to a slower growth kinetics caused by a low calcium value present in this rock.