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.
Transverse and compressional (longitudinal) waves are similar because have a frequency (and therefore a period), and a wavelength. that can be calculated. Waves come in either two major categories: electromagnetic or mechanical. Electromagnetic waves are light waves. They are energized particles that travel very quickly. They do not need a medium to travel, which means that they can travel through outer space where there is no matter. Mechanical waves are waves that require a medium (matter) to travel. These waves are considered to have two major shapes: transverse and compressional. For waves we can peform calculations using two equations: Frequency is the inverse of the time it takes for one cycle of the wave to occur.