Nonetheless, large amounts of asphalt occur in concentrated form in nature.
Naturally occurring deposits of bitumen are formed from the remains of ancient, microscopic algae (diatoms) and other once-living things.
In American English, "asphalt" (or "asphalt cement") is commonly used for a refined residue from the distillation process of selected crude oils.
Outside the United States, the product is often called "bitumen", and geologists worldwide often prefer the term for the naturally occurring variety.
Common colloquial usage often refers to various forms of asphalt as "tar", as in the name of the La Brea Tar Pits.
Naturally occurring asphalt is sometimes specified by the term "crude bitumen".
Most natural bitumens also contain organosulfur compounds, resulting in an overall sulfur content of up to 4%.In American English, "asphalt" is equivalent to the British "bitumen".However, "asphalt" is also commonly used as a shortened form of "asphalt concrete" (therefore equivalent to the British "asphalt" or "tarmac").From the same root is derived the Anglo-Saxon word cwidu (mastix), the German word Kitt (cement or mastic) and the old Norse word kvada.In British English, "bitumen" is used instead of "asphalt".