Light micrograph of a polished surface of a lithotype clarain (bituminous coal) which shows a fine lamination mark by inertinite and vitrinite group macerals and clay. We can see funginite in the upper right corner, and fusinite in the center left (clear macerals). The dark gray and black structures with rounded shape, are bubbles (artifacts). The coal is a sedimentary rock that occurs in stratified deposits: dead vegetation burried deep in the earth, during the Carboniferous Period, due to the high temperature and pressure, was slowly converted to coal. The solar energy stored by the plants trough the photosynthesis was located inside the coal. And it is released again during combustion. Coal is the largest source of energy in the production of electricity worldwide. Nevertheless it produces importants environmental and health effects. The clean coal technology is developed to mitigate harmful emissions to the atmosphere. Field of view size: 2.97 x 4.45 mm (0.117 x 0.175 in)