Asphalt is the heaviest fraction of petroleum, left behind when the more volatile compounds evaporate. It flows slowly during warm weather and may be stiff enough to shatter during cold times. Geologists use the word “asphalt” to refer to what most people call tar, so technically this specimen is asphaltic sand. Its underside is pitch-black, but it weathers to a medium gray. It has a mild petroleum odor and can be crumbled in the hand with some effort. A harder rock with this composition is called bituminous sandstone or, more informally, tar sand.
Asphalt is a brownish-black semisolid or solid mixture of bitumen, either from a native source or as a petroleum by-product. Sometimes the term asphalt refers to a mixture of asphalt with sand, gravel or crushed stone.
Asphalt is a natural or artificial mixture in which bitumen is associated with inert mineral matter. It is black or brownish black in color. At temperature between 50–100°C it is in liquid state whereas at temperature less than this it remains in solid state. Because it is a thermoplastic material it softens as it is heated and hardens as it is cooled. It is the basic paving material in use today.