ABSTRACT
Glass has been dened by the ASTM (2010) as “an amorphous, inorganic product of fusion that has been cooled to a rigid condition without crystallizing.” Although glass is often regarded as a synthetic material, it was formed naturally from common elements in the earth’s crust long before the world was inhabited. Natural materials such as obsidian (from magma or molten igneous rock) and tektites (from meteors) have compositions and properties similar to those of synthetic glass; pumice is a naturally occurring foam glass.
