Found at the surface of a lava flow, pumice stone is volcanic glass formed by the solidification of lava that is permeated with gas bubbles. It's light grey and looks like a normal rock.
It's often left in this form, which most people will recognise.
It's used widely in soap making - a great ingredient that helps to remove dirt. We've used it in our Fresh Feets foot soak, which is really cooling. Pumice powder adds another dimension - soothing and softening feet!