The researchers studied different types of Ombilin coals by looking at their composition under a microscope. They found that the coals are mainly made up of vitrinite, with some other materials like exinite, inertinite, and minerals. The type of coal and its quality are influenced by the climate and peat conditions where it formed. Some coals have higher vitrinite reflectance due to heat from underground activity. The coals affected by heat have more vitrinite and are at a more advanced stage of coal formation compared to those not affected by heat. Heat also makes it harder to distinguish between different types of materials in the coal.