The study looked at different types of coal from Western Indonesia to see how they were formed. By examining the coal under a microscope, the researchers found that the coals were mainly made up of vitrinite, liptinite, and some inertinite. The type of coal depended on the climate and conditions where it formed. Even though the coals are young in geological terms, they showed different levels of coalification. This was due to the depth they were buried at and the effects of volcanic activity in the area.