Sapropelic Coal

(also sapropelite), a solid combustible mineral that occurs as a result of the transformation of the remains of lower animals and plant organisms under the conditions of lake or lagoon facies. Sapropelic coal is distinguished from humic coal, or humolite, which is the product of the decay of the remains of higher plants under the conditions of swamp facies.

Sapropelic coals are massive tough rocks that are brown, brownish gray, or black in color and have a dull or greasy luster; the fracture is subconchoidal. The following classes of sapropelic coals are distinguished: sapropelic coals proper, which include boghead coals and saprocols, humic sapropelic coals, which include cannel boghead coals, cannel coal kassianites, and cheremites, and sapropelic humic coals, which include cannel coals and kasianites.

Sapropelic coals are classified on the basis of the quantitative ratios between their sapropelic (alginite) and humic (vitrinite, fusinite, and lipetinite) microcomponents. The kerogen of sapropelic coals is characterized by its chemical and material composition, which reflects the content of elements of lipid, carbohydrate and protein, and lignin and cellulose origin. In sapropelic coals proper, lipids that are primarily in the form of polymer lipids predominate. During metamorphosis they are broken down into components capable of migration; the remaining substance is similar to humus.

Sapropelic coals are distinguished from humic coals by a higher output of volatile substances (60–90 percent) and primary tar (more than 50 percent), a higher hydrogen content (7–12 percent), and greater combustion heat. Sapropelic coals are a particular type of rock with sapropelic kerogen, corresponding to varieties with a higher content of organic matter.

Sapropelic coals are found in coal deposits in the brown coal, long-flames, and gas stages of coalification. They are found in the Moscow and Irkutsk coal basins in the USSR and the Ruhr Coal Basin in West Germany. In other coal basins they are found as independent strata or distinct layers in humic coals and are extracted incidentally. Liquid fuel is obtained from sapropelic coals. Tenacious sapropelic coals have been used as fabricating material.