Clay is used on baseball and softball fields in the base paths, batter's boxes, bullpens, pitcher's mounds, and practice areas. If used by itself, however, clay is not an ideal surface for play. In the early days of baseball, the clay infield would become as hard as concrete in the summer heat and a slippery marsh after a rain storm. One improvement in the evolution of field clay is calcined clay, which is clay that has been heated in a furnace at about 2,000º F. Once calcined, the clay is ground into a powder that readily absorbs water, reduces soil compaction, and will not stick to cleats. This type of product is used as an infield conditioner and to dry wet spots on a field or track quickly. For more information about clays, visit http://minerals.usgs.gov/minerals or http://minerals.usgs.gov/minerals/pubs/general_interest/sport_mins/clay_surfaces.pdf , or contact Robert Virta at (703) 648-7726 or rvirta@usgs.gov .