History of applied coal petrology in the United States. IV. Reflections on the centennial of the introduction of coal petrology to North America

Reinhardt Thiessen introduced a thin-section-based, botanically oriented method of coal petrology to North America in 1920. The nomenclature derived from this system, although eventually reconciled with and largely superseded by the European reflected-light techniques and nomenclature, persisted for decades after Thiessen's death in 1938. The research by Thiessen and his colleagues at the U.S. Bureau of Mines was the foundation of applied coal petrology in the United States, with research on the preparation, coking, and hydrogenation properties of coals. Thiessen's botanical training enabled him to recognize distinct spores in coals. Although he did not macerate the samples and he did not provide genus and species names, the demonstration that he could use spores to correlate coals through the Northern Appalachian coal basin provided a foundation for regional stratigraphic palynology. Homer Turner, an American geologist and fuel scientist, was a pioneer in the petrographic study of anthracite. Using a method of etching polished blocks of anthracite, he developed a parallel approach to Reinhardt Thiessen's studies of thin sections of bituminous and lower-rank coals, describing well-preserved botanical structures. This, in turn, supported the view that anthracite just had a higher degree of metamorphism than bituminous coals, opposed to the older view that anthracite had a different botanical origin. In a joint study with the U.S. Bureau of Mines, Turner produced a map of equal volatile matter contours (isovol) across the Pennsylvania Anthracite Fields. He was also a collaborator in a study on the X-ray diffraction structure of anthracite, presaging better known studies by Rosalind Franklin and others.