Coal | National Geographic Society
Dec 22, 2012· Today, almost a third of American coal mines use longwall mining. Outside the U.S., that number is even higher. In China, the world's largest coal producer, more than 85% of coal is exracted using the longwall method. Underground Mining: Room and Pillar In the room-and-pillar mining method, miners carve a "room" out of coal. Columns ...