Coal is a rock derived from plants are dead and buried by silt, sand and clay over millions of years. The existence of high-temperature soil pressure and the occurrence of tectonic movements resulted in the burning or oxidation that converts wood substance in plants carcass into combustible rock called coal.
In Indonesia there are large coal mines such as mine Sawahlunto ombilin in West Sumatra and acid mine hill in southern sumatra. Several kinds / types of coal mining method:
1. Open Pit MiningCoal mining activities without doing heavy digging because the location of coal near the surface of the earth.
2. Underground MiningTo mine coal with these techniques must be made a straight tunnel to reach the coal seam. Furthermore, the tunnel is made flat to mine.
3. Deep MiningMining coal is done when the area was under the hill where made sloping tunnel to reach coal seams.
4. Above Surface MiningType of coal mining activities are carried out if the targeted coal is in the belly of the hill, the flat tunnel where necessary in order to begin mining the coal.