Product

Subbituminous coal is a medium-rank coal intermediate between lignite and bituminous coal, characterized by 42-52% carbon content (dry, ash-free basis) and calorific values of 4,540-6,200 kcal/kg (19-26 MJ/kg). It appears dark brown to black with a dull to moderate luster, and while lower-rank subbituminous C resembles brown lignite, higher-rank subbituminous A grades appear gray-black and shiny like bituminous coal.

Sub-bituminous rank and defining characteristics ^[3]

The coal contains 10-25% moisture, significantly less than lignite but more than bituminous coal, making it harder and more suitable for transportation and storage. Subbituminous coal has higher volatile matter content than bituminous coal and notably low sulfur content, often below 1%, which reduces environmental emissions despite its lower heating value. The woody cellular structure visible in lignite is absent, replaced by alternating dull and bright vitrinite bands similar to bituminous coal patterns.

Subbituminous coal is non-agglomerating and does not form coke during combustion. It represents approximately 30% of global coal resources and is geologically younger, ranging from 251 million years old to recent formations. Due to its lower calorific value compared to bituminous coal, larger quantities must be burned to produce equivalent energy, though many power plants have adopted it specifically for its low sulfur emissions profile.

References

1. Jay Ganesh Minerals. Bituminous vs Lignite Coal: Key Properties and Uses (Sep 7, 2025)
2. Raha Gilsonite Co.. Bituminous coal (Aug 14, 2017)
3. Kentucky Geological Survey, University of Kentucky. Sub-Bituminous Coal
4. Kopp O.C.. subbituminous coal (page version: Sep 13, 2019). Britannica
5. Energy Education Canada. Sub-bituminous coal
6. U.S. Environmental Protection Agency (EPA). Bituminous And Subbituminous Coal Combustion (Sep 2020)
7. Kay A. (Nov 29, 2017). Coal 101: Sub-bituminous Coal Explained. Investing News Network