The stalactites (rock icicles) hanging from cave ceilings, stalagmites
built up from the floors, and other drip stone deposits of caves are
largely calcite, the mineral of limestone. Again, this can be recognized
by the limestone acid test (effervescence, see limestone). Cave onyx may
be banded like agate. It is then commonly called Mexican onyx. The name
travertine has also been applied to such deposits from water.