Answer:
high temperature and high pressure
Explanation:
Coal is one of the solid minerals found underground. Coal is believed to have been formed from vegetation during the carboniferous era. The decomposition of these materials under pressure in the absence of air led to the formation of coal.
In the process of carbonization, the vegetation was converted in stages to peat, lignite, bituminous coal and anthracite.
The formation of anthracite is favored by high temperature and high pressure underground.
