Fireclays are sedimentary mudstones which occur as seatearths or fossil soils that underlie almost all coal seams. Originally valued as refractory raw materials, fireclays are now primarily an essential raw material for the manufacture of buff and pale-bodied bricks, clay pipes and other ceramics.

Fireclays are mainly confined to the Coal Measures.

Most fireclays are relatively thin and extraction on their own would not be economically viable because of high overburden to mineral ratios. Surface coal mining sites are the main source of supply, currently accounting for some 90 per cent.

Fireclay supply is thus highly dependent on surface mining operations