Vitrinite refletance
Vitrinite is a maceral group derived from the remains of woody material from vascular plants and is composed of thermally evolved products of lignin and cellulose. Vitrinite is the dominant component of humic coal and is also found dispersed in sedimentary rocks. Vitrinite reflectance analysis (Ro%, Roran%, VR%) is the microscopical determination of the reflectance of incident light from vitrinite, in immersion oil (refractive index 1.518 at 546 nm and 23 °C) calibrated according to known reflectance standards (Klein & Becker GmbH & Co. KG) and following ASTM D7708 procedures. The random reflectance of vitrinite increases systematically with increasing thermal maturation during burial and heating of sedimentary rocks, and this property allows vitrinite reflectance analysis to be used as a common geothermometer for source rocks in petroliferous basins. Vitrinite reflectance analysis also is used as a method to determine coal rank.