Exinite

In coal geology, exinite is an umbrella term, used when referring to the finely-ground and macrerated remains, originally formed by spores, pollen, dinoflagellate cysts, leaf cuticles, plant resins and waxes, as found in coal deposits. Exinite is one of the four categories of kerogen.

M.C. Stopes introduced the term exinite in 1935 to describe the microscopic constituent of coal, rich in volatiles and relatively rich in hydrogen, that is represented by the exines of spores. C.A. Seyler in 1932, however, used the term with its present meaning, designating the following group of macerals: sporinite, cutinite, alginite, resinite.

Macerals (from the same Latin source as 'macerate') are to coal as minerals are to rock. The term was coined by M. C. Stopes in 1935, who wrote

"The concept behind the word ‘macerals’ is that the complex of biological units represented by a forest tree which crashed into a watery swamp and there partly decomposed and was macerated in the process of coal formation, did not in that process become uniform throughout but still retains delimited regions optically differing under the microscope, which may or may not have different chemical formulae and properties. These organic units, composing the coal mass I propose to call macerals, and they are the descriptive equivalent of the inorganic units composing most rock masses and universally called minerals." (in Fuel in Sci. & Pract. XIV (1935) 11/1).

The macerals grouped under the term exinite are not necessarily entirely composed from exines, but appear to have similar technical properties, though little information is so far available on the technological behavior of pure exinite.