Forever. As long as the rock chambers holding the air don't break, there is no reason for it to sink. If the piece is too small and is depending on air in the outer edges to hold it up, once the air goes out of them, it might lose its bouyancy.
Pumice.
In general, pumice will float. There is enough trapped air in pumice that it is buoyant.
Any with a density less than the fluid into which it is placed. Pumice is a volcanic rock that will sometimes float on water.pumice
Pumice rocks have been known to float across oceans.
Pumice is able to float.
It can float.
The pumice is not very dense, if the mass of the volume of water displacement is greater than the mass of the rock it will float
Pumice.
it has holes in it and has kelfrigis
No, but pumice can.
Pumice.
one. Pumice.