Moonmilk

Moonmilk (sometimes called mondmilch, German for moonmilk, sometimes wrongly montmilch, or also cave milk) is a white, creamy substance found inside caves. It is similar to other deposits, but its unique quality is that it does not harden or turn to stone. It is a precipitate from limestone comprising aggregates of fine crystals of varying composition usually made of carbonate materials, e.g., calcite, hydromagnesite, and monohydrocalcite.