A term applied to white formless
pasty or powdery masses
found in
caves, sometimes wet with
cheese-like consistency,
sometimes dry masses of sticky powder; composed of several
carbonate minerals. The mechanism by which the organisms
break down the
calcite and redeposit it as moonmilk has not
been determined. A
bacterial origin seems probable for some
moonmilk.
From: http://www.nps.gov/cave/glossary.htm#I