1.   ...the traditional method of pick and shovel to extract coal.

2.   The process can take months before all the accessible coal is extracted.

3.   Very simply put, miners no longer extract coal from the mountain.

4.   Coal companies in Appalachia have been turning to mountaintop mining as an inexpensive way to extract coal.

5.   The top of a ridge is sheared off, the coal is extracted, and the leftover rock and dirt are pushed into a nearby river valley.

6.   Vietnam extracts coal mainly from open-cast mines in mountainous parts of the northern province of Quang Ninh.