The pore spaces (known as vesicles) in pumice are a clue to how it forms. The vesicles are actually gas bubbles that were trapped in the rock during the rapid cooling of a gas-rich frothy magma. The material cools so quickly that atoms in the melt are not able to arrange themselves into a crystalline structure.Thus, pumice is an amorphous volcanic glass known as a  mineraloid .he abundant vesicles in pumice and the thin walls between them give the rock a very low specific gravity. It typically has a specific gravity of less than one, giving the rock an ability to float on water.
While an electromagnetic wave is called just a disturbance, a mechanical wave is considered a periodic disturbance. Mechanical waves are also called elastic waves as their propagation depends on the elastic properties of the medium through which the waves pass.
Rather, we are talking about the waves that transmit radio signals. The main difference between radio waves and sound waves is that radio waves are a type of electromagnetic wave that can travel when there is no medium, whereas sound waves are a type of mechanical wave that cannot travel if there is no medium. What are Radio Waves. Radio waves are electromagnetic waves. These are waves composed of electric and magnetic fields, which are oscillating at right angles to each other. The energy of an electromagnetic wave propagates at a direction at right angles to the oscillations in both the electric and magnetic fields.