Kentucky mines coal, limestone, clay, sand and gravel. Coal mining operations are carried out mainly in the Western Kentucky Coal Field and the Eastern Kentucky Coal field. As to nonfuel minerals, Mississippian limestones are mined in the Mississippian Plateaus Region and along Pine Mountain in southeastern Kentucky. Ordovician and Silurian limestones are mined from the central part of the state. Clay minerals that are mined in the state include common clay, ceramic and ball clays, refractory clay and shale. Just like in 2004, mining activities in the state remain significant.