Fireclay

Extraction

Unlike conventional brick-making clay, some fire clays (especially flint clays) are mined at depth, found as a seatearth, the underclay associated with coal measures. Though many are extracted through open pit methods. Many fireclay deposits are associated with coal even if the seam is small and of low quality but not all fire clays form around coal. While many commercial mines focus on huge deposits sometimes spanning 100s of miles wide and meters thick found in sedimentary rocks associated with coals, formed by primary clay that has been eroded and transported downstream in a somewhat pure form or has been chemically weathered after deposition(from ground water itself or from the organic acids from said coal) . These deposits are similar to ball clay deposits in every way except iron content, particle size, and fired color . Although smaller deposits occur in innumerable spots across almost every U.S. state, as well as every country, these can occur as primary clay deposits from chemical weathering, much like kaolin deposits but from parent rocks with more iron. More commonly they occur in a wide variety of sedimentary rocks and can vary quite differently in terms of plasticity, color, sand content, and mineral content and can be found next to or within meters of clays of other or similar types. Many of these deposits were abandoned during the turn of the 20th century and lay abandoned still or covered by development .