Calcite moonmilk: Crystal morphology and environment of formation in cavesin the Italian Alps

Calcite moonmilk, which is a cave deposit formed of calcite crystals and ma ter, is found in many caves in the Italian Alps. These modern and ancient d eposits are formed of fiber calcite crystals, 50-500 nm wide and 1 to > 10 mu m long, and polycrystalline chains that have few crystal defects. Radioc arbon dating indicates that most moonmilk deposits in these caves are fossi l and that for most precipitation ceased similar to 6400 cal years BP, at t he end of the mid-Holocene Hypsithermal, In the caves of the Italian Alps, the optimal conditions for formation of c alcite moonmilk are: (1) a temperature range of 3.5-5.5 degrees C, (2) low discharge volumes of seepage waters that are slightly supersaturated (SICAL = 0.0 to similar to 0.2), and (3) relative humidity that is at or close to 100%. Microbial activity apparently did not play an active role in the for mation of the calcite moonmilk, Conditions for moonmilk formation are typic ally found in caves that are located beneath land surfaces, which are soil covered and support a conifer forest. Precipitation of the fiber calcite cr ystals apparently involved very slow how of slightly supersaturated fluids. The fact that moonmilk appears to form under a narrow range of environmenta l conditions means that this cave deposit has potential as a paleoclimatic indicator in high alpine karst areas.