Silt three grades fine, medium and coarse 0.002 mm to 0.006 mm to 0.020 mm to 0.063 mm). In actuality, silt is chemically distinct from clay, and unlike clay, grains of silt are approximately the same size in all dimensions; furthermore, their size ranges overlap. Clays are formed from thin plate-shaped particles held together by electrostatic forces, so present a cohesion. Pure silts are not cohesive. According to the U.S. Department of Agriculture Soil Texture Classification system, the sand–silt distinction is made at the 0.05 mm particle size. The USDA system has been adopted by the Food and Agriculture Organization (FAO).
Gravel Ridge, Arkansas $44,318. Males had a median income of $31,553 versus $21,903 for females. The per capita income for the CDP was $16,932. About 7.9% of families and 8.5% of the population were below the poverty line, including 10.6% of those under age 18 and 12.9% of those age 65 or over. The climate in this area is characterized by hot, humid summers and generally mild to cool winters. According to the Köppen Climate Classification system, Gravel Ridge has a humid subtropical climate, abbreviated "Cfa" on climate maps. Gravel Ridge, Arkansas Gravel Ridge is a former census-designated place (CDP) in Pulaski County,