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Rock asphalt is a naturally occurring mixture of rock and asphalt (a petroleum product) that can be mined and used directly for paving roads. It matters because it provides a ready-made source of asphalt material without requiring the processing and mixing that conventional asphalt production demands.
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Natural bitumen from the Dead Sea Refined bitumen The University of Queensland pitch drop experiment, demonstrating the viscosity of bitumen
Bitumen ( UK: /ˈbɪtʃʊmɪn/ BIH-chuum-in, US: /bɪˈtjuːmɪn, baɪ-/ bih-TEW-min, by-) is an immensely viscous constituent of petroleum. Depending on its exact composition, it can be a sticky, black liquid or an apparently solid mass that behaves as a liquid over very large time scales. In American English, the material is commonly referred to as asphalt. Whether found in natural deposits or refined from petroleum, the substance is classed as a pitch. Prior to the 20th century, the term asphaltum was in general use. The word derives from the Ancient Greek word ἄσφαλτος (ásphaltos), which referred to natural bitumen or pitch. The largest natural deposit of bitumen in the world is the Pitch Lake of southwest Trinidad, which is estimated to contain 10 million tons.