Light weight and very porous, this volcanic rock (pumice?) is perfect for terrarium, paludarium, or vivarium plantings.  It holds water like a sponge and can be used with or without the enclosed pump. The use of the pump will require a sump in your setup in which to place it.  The footprint of this piece is a bit less than a standard 2-1/2 gallon tank.

Since this rock actually floats, it may not be suitable for an aquarium.  Plus, the many sharp glassy edges could easily damage fish.  Take care when handling!