Asphalt, black or brown petroleum-like material that has a consistency varying from viscous liquid to glassy solid. It is obtained either as a residue from the distillation petroleum or from natural deposits. Asphalt consists of compunds of hydrogen and carbon with minor proportions of nitrogen, sulfur, and oxygen. Natural asphalt (also called brea), which is believed to be formed during an early stage in the breakdown of organic marine deposits into petroleum, characteristically contains minerals, while residual petroleum asphalt does not.
The use of asphalt is very old, dating back to its use as a water stop between brick walls of a reservoir at Mohenjo-Daro (about the 3rd millennium BC) in Pakistan. In the Middle East it was extensively used for paving roads and sealing waterworks, important applications even today.
