Vitrinite

Vitrinite is one of the primary components of coals and most sedimentary kerogens. Vitrinite is a type of maceral, meaning organic components of coal analogous to the "minerals" of rocks. Vitrinite has a shiny appearance resembling glass (vitreous). 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 and forms diagenetically by the thermal alteration .

Vitrinite is common in sedimentary rocks that are rich in organic matter, such as shales and marls with a terrigenous origin, or some terrigenous content. Conversely, carbonates, evaporites and well-sorted sandstones have very low vitrinite contents. Vitrinite is absent in pre-Silurian rocks because land plants had not yet evolved.

Vitrinite reflectance (Ro%) is an important geochemical parameter used to assess and evaluate the thermal maturity of sedimentary rocks, particularly those rich in organic matter, such as shales. Ro% can be determined under oil immersion using a reflected light microscope in which the amount of light reflected is measured by a sensor, such as a photomultiplier tube, and is expressed as percent reflected from polished vitrinite. Vitrinite reflectance increases with greater burial depth and thermal exposure, roughly doubling every 10 C°, making it a reliable indicator of the maximum temperature a rock has experienced during its geological history. Ro% can indicate if and what types of hydrocarbon(s) could be formed but it cannot determine when the generation process started or how much there is.