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.
Mechanical Waves are waves which propagate through a material medium (solid, liquid, or gas) at a wave speed which depends on the elastic and inertial properties of that medium. There are two basic types of wave motion for mechanical waves: longitudinal waves and transverse waves.The animations below demonstrate both types of wave and illustrate the difference between the motion of the wave and the motion of the particles in the medium through which the wave is travelling.ater Waves. Water waves are an example of waves that involve a combination of both longitudinal and transverse motions. As a wave travels through the waver, the particles travel in clockwise circles. The radius of the circles decreases as the depth into the water increases.