What's the noun for coalfield? Here's the word you're looking for.
coal
(uncountable) A black rock formed from prehistoric plant remains, composed largely of carbon and burned as a fuel.
(countable) A piece of coal used for burning. Note that in British English either of the following examples could be used, whereas the latter would be more common in American English.
“The Coalsack Nebula is the most prominent dark nebula in the skies, easily visible to the naked eye as a prominent dark patch in the southern Milky Way.”
“The Kalapalo people of Mato Grosso state in Brazil saw the stars of Crux as Aganagi angry bees having emerged from the Coalsack, which they saw as the beehive.”
“After the first half of the expedition, Vespucci mapped Alpha and Beta Centauri, as well as the constellation Crux, the Southern Cross and the Coalsack Nebula.”
“His father, a farmer and owner of a small coalpit, returned each morning from his walk to the colliery with glowing reports of what he had seen in the landscape.”
“It was the year of the Cannock coalpit explosion tragedy, the year British airship R101 crashed in France, and the year in which Princess Margaret was born.”
“It was found on fire around two hours later at Coalpit Lane, Denaby, and has since been recovered by police for forensic examination.”
coalification
(geology) The formation of coal by the gradual heating and compression of organic matter, normally via peat
“There was Mr Fox and his trucks carting coal from the pitheads and they were held not to be in the coalmining industry.”
“This is a benevolent fund, to which the coalmining companies contribute an amount that is levied on them, for the benefit of miners and their families, and the community.”
“Industrial expansion here depended on coalmining and iron working.”
“Standing at Xiangjiaba village, 370m below one sees coalers and cement carriers stream up and down a narrow channel off the far bank.”
“The fleet was accompanied for parts of the tour by auxiliaries including supply ships and coalers.”
“In the March 2001 issue Sir Ranulph Fiennes, the Polar explorer, is Guest Editor and articles include a look at the plight of the albatross and Britain's sea coalers.”