Complex mixture of compounds with large molecules containing mainly hydrogen and carbon but also oxygen, nitrogen, and sulfur. Kerogen is a precursor of petroleum and the organic component of oil shales. It is waxy and insoluble in water; upon heating, it breaks down into recoverable gaseous and liquid substances resembling petroleum. It consists of compacted organic material, such as algae and other low plant forms, pollen, spores and spore coats, and insects.

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