Vitrinite is a type of maceral, where "macerals" are organic components of coal analogous to the "minerals" of silicate rocks.
Vitrinite has a shiny appearance resembling glass. It is derived from the cell-wall material or woody tissue of the plants from which coal was formed. Chemically, it is composed of polymers, cellulose, and lignin.
Since vitrinite changes predictably and consistently upon heating, its reflectance is a useful measurement of source rock maturity.
Because vitrinite originated in wood, its occurrence in marine rocks may be limited by the depositional processes that act in a given depositional environment.
*Kerogen is the naturally occurring, solid, insoluble organic matter that occurs in source rocks and can yield oil upon heating. Typical organic constituents of kerogen are algae and woody plant material.