Rock Phosphate is a mined rock that contains limestone, silica and clay as well as high concentration of phosphorus. Being a natural compound, Organic Material Review Institute (OMRI), USA listed rock phosphate in organic farming, agriculture, gardening and food production. Rock phosphate is the cheapest source of phosphorus.
· The Ashley Formation, or Ashley limestone informally, is about 20+ meters thick, and composed of olivetan sandy limestone with occasional greensand; the base of the unit contains a phosphate lag. This is the thicker of the two Oligocene units in the area; it is overlain by the patchy and thin (one meter at most) Chandler Bridge Formation.