Kerogen

Kerogens are chemical compounds formed by the low-grade metamorphism (i.e. diagenesis) of organic molecules derived from decaying plant and animal matter.

Kerogens are the precursors to hydrocarbons (fossil fuels). Labile kerogen breaks down to form heavy hydrocarbons (i.e. oils), refractory kerogen breaks down to form light hydrocarbons (i.e. gases) and inert kerogen forms graphite.