Kerogen is a mixture of organic chemicals present in sedimentary rocks. They are insoluble in common organic solvents, due to their enormous molecular weight (above 1,000 Daltons). The soluble portion is known as bitumen. When heated within the earth's crust (oil window at about 60 ° -120 ° C, natural gas window at about 120 ° -150 ° C) some types of kerogen give off crude oil or natural gas, known collectively such as hydrocarbons (fossil fuels). When such querógenos are present in high concentrations in rocks such as the slate, it is possible that they are mother rock. Chalk-rich slates that have not been subjected to sufficient temperature to release hydrocarbons may form deposits of bituminous slate.
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