Coal petrology studies different types of plant remains in coal, called macerals, which are classified into vitrinite, liptinite, and inertinite. Vitrinite-rich coals form in wet conditions, inertinite-rich coals form in dry conditions, and liptinite comes from swampy areas. By studying the optical properties and quantities of these macerals, we can understand the chemical properties of coal and predict its uses. Currently, researchers are using petrology to determine if coal can produce methane gas during its formation process.