Glass, the material

When considered as a material, glass is a collective term for an unlimited number of materials of different compositions in a glassy state. Glassy materials can also occur naturally. For example, obsidian, often found in volcanic areas, has a composition comparable to man-made glass. It consists of sand, and sodium and calcium compounds; and it was fashioned into knives, arrowheads, spearheads, and other weapons in ancient times. Natural glass in the form of obsidian was primarily used by peoples of the Eastern Mediterranean. It was in high demand in this region as an object of trade. The Aztecs in Mexico were also familiar with obsidian and created religious and household items from it.