During which geologic period did most anthracite and bituminous coal deposits form?

Most anthracite and bituminous coal deposits formed during the latter half of the Paleozoic Era, specifically within the Carboniferous Period (358.9 million to 298.9 million years ago) and the Permian Period (approximately 298.9 million to 251.9 million years ago).1

During the Carboniferous Period, extensive bituminous coal deposits formed across eastern North America and Europe. In contrast, many of the coal deposits found in Siberia, eastern Asia, and Australia are of Permian origin. These periods provided the warm, humid climates and low-lying coastal environments necessary for the accumulation of the plant matter that eventually transformed into these higher-rank coals through metamorphism and compaction.12