Reigate Stone is a freestone that was mined from the Upper Greensand in north east Surrey. It was used in building work throughout the middle ages and early modern period. It is sometimes classified as a calcareous sandstone, although very little of the silica content is in the form of detrital sand grains. In addition to silicon dioxide, the stone also includes clay, fine-grained calcite, mica flakes and glauconite.