It is one of the key indicators for identifying the type and quality of coal
Under constant surface temperatures and pressure, the remains of plants accumulated in stagnant water are converted from peat or decomposition to peat or decomposition; peat or decomposition, when buried, sink to the depths of the ground as a result of the decline in the base of the basin, transform into brown coal by rocking; and when temperature and pressure are gradually transformed into smoke-free coal by deformation coal
