1. Mineral Commodities Solid Earth System

15. Coal Mining Techniques

22. Mine was using ‘retreat mining’ where pillars of coal, originally left to hold up the mine’s roof, are removed, in order to recover the coal in them. The pillars near the back of the mine are removed first, hence the word ‘retreat’. Ideally, the roof collapses in a sequence of small events. But if collapse is delayed, it can be very energetic and dangerous.

24. Black Lung Disease

27. Mountaintop removal coal mining

28. Mine leachate near Ouray CO

30. froth flotation tank

34. pouring slag at night