Coal is a firm, brittle, and easily combustible sedimentary rock derived mainly from compacted plant debris, including ferns and club mosses. Depending on its quality, or grade, coal is divided into three main categories: anthracite, bituminous, and lignite. Anthracite, the hardest and highest-grade coal, is not found in Kansas.
Bituminous coal, the most common type in Kansas, is found mainly in the eastern third of the state. It breaks into irregularly shaped blocks, has a luster varying from dull to fairly bright, and burns with a yellow flame. Bituminous coal was mined continuously in the state from 1869 until early 2016, when the last strip-mining operation in Linn County shut down.
Lignite, often referred to as brown coal, is found in small deposits in north-central Kansas. Because it has a high water content and well-preserved plant structures, lignite crumbles when exposed to air. It was mined in small quantities as late as 1940 in north-central Kansas from the Cretaceous-age Dakota Formation.
Most coal in Kansas formed from swamp muck during the Pennsylvanian subperiod, sometimes called the "Great Coal Age." At that time, widespread freshwater swamps in eastern Kansas covered low-lying areas thick with ferns as tall as trees and other primitive plants. Layers of dead and decaying plants accumulated on the bottom of the swamps and were eventually covered by layers of mud and sand. The weight of the overlying layers compressed the plant debris.
Over time, the decaying plant material formed into peat—a soil-like partially decayed mineral matter—then lignite, then bituminous coal, then anthracite. Geologists estimate that it took about 10 feet of leaves, tree trunks, and other organic matter to produce a one-foot layer of coal.
Brady, L. L., and Hatch, J. R., 1997, Chemical Analysis of Middle and Upper Pennsylvanian Coals from Southeastern Kansas: Kansas Geological Survey, Current Research in Earth Sciences, Bulletin 240, p. 43-59.
Buchanan, R., 2010, Kansas Geology: An Introduction to Landscapes, Rocks, Minerals, and Fossils (2nd ed.): Lawrence, Kansas, University Press of Kansas, 240 p.
Buchanan, R., and McCauley, J. R., 2010, Roadside Kansas: A Traveler's Guide to Its Geology and Landmarks (2nd ed.): Lawrence, Kansas, University Press of Kansas, 392 p.
Kansas Rocks and Minerals, Kansas Geological Survey Educational Series 2