complex mixture of compounds with large molecules containing mainly hydrogen and carbon but also oxygen, nitrogen, and sulfur. It is the organic component of oil shales (oil shale), hence their alternative names of kerogen shales or kerogenites. Kerogen is insoluble in water; upon heating, it breaks down into recoverable gaseous and liquid substances resembling petroleum. It may consist of compacted organic material, such as algae and other low plant forms, pollen, spores and spore coats, and both adult and larval insects. The name was first applied to oil-bearing shales in Scotland.