.]]]] Gravel is rock that is of a certain particle size range. In geology, gravel is any loose rock that is at least two millimeters (2mm) in its largest dimension (about 1/12 of an inch) and no more than 75 millimeters (about 3 inches). Sometimes gravel is restricted to rock in the 2-4 millimeter range, with pebble being reserved for rock 4-75 millimeters (some say 64 millimeters). The next smaller size class in geology is sand, which is 0.063 mm to 2 mm in size. The next larger size is cobble, which is 75 (64) millimeters to 256 millimeters (about three to ten inches). One cubic foot (28.32 dm^3) of gravel typically weighs about 100 pounds (45 kg) [LINK: http://www.recyclemaniacs.org/doc/measurement-tracking/conversions.pdf] [1]. Gravel is an important commercial product, used in many applications. Many roadways are surfaced with gravel, especially in rural areas where there is little t