Silicon (named from silex or flint) is the 14^th element.  It is not classified as a metal but displays many metal-like properties.  It is properly called a semimetal or metalloid.  It is used to make semiconductors that have an electrical conductivity intermediate between metals and nonmetals.  It is the second most abundant element and makes up about 25% of the earth’s crust.  Sand is mainly composed of silicon dioxide.

Synthetic glass was originally prepared by heating a mixture of sodium oxide (or sodium carbonate), calcium oxide and silicon dioxide (sand).  Obsidian, a black volcanic glass, is probably the best known of the naturally occurring glasses.  It was used by early man to form cutting tools, arrowheads and spearheads.