Rock asphalt and gilsonite

Rock asphalt is natural asphalt found in solid form. It was formed millions of years ago when layers of petroleum harden after heavier components settled while lighter components evaporated. The hardening took place, in most of the cases, within the pores of rocks (mainly limestone or sandstones) thus, a number of mineral materials are normally found within rock asphalt. 

Rock asphalt, as natural asphalt in liquid-viscous form, was used historically in engineering works but today its use in road works is rare. Rock asphalt nowadays is used only as an additive to petroleum bitumen. Since it is a very hard material, its use is to harden petroleum bitumen. 

The largest natural surface deposits of rock asphalt that are commercially exploited are found in Utah in the United States (28 km ) and Kermanshah in Iran. 

The rock asphalt in the Uintah Basin in Utah has the trade name gilsonite, from S.H. Gilson, the founder of a mining company in 1888. 

Gilsonite today is a well-known additive for hardening petroleum bitumen. 

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