The researchers studied coal samples from East Kalimantan to understand their composition and formation. They found that the coals were mainly formed under wet conditions, with high vitrinite content indicating a brighter lithotype. The presence of pyrite and calcite suggests a marine environment during coal deposition. Differences in coal types were due to variations in peat accumulation periods and geological settings. The coal ranks ranged from subbituminous A to high volatile bituminous C, influenced by the thickness of cover during coalification.