Rock phosphate is a naturally occurring mineral that is mined and used as a phosphorus fertilizer. It contains calcium phosphate in the form of fluorapatite, with the chemical formula Ca5(PO4)3F. The document provides specifications for two types of rock phosphate - 28% P2O5 and 30% P2O5 - listing elemental composition ranges, acceptable limits for contaminants, required solubility in acids, color, and particle size distribution. Rock phosphate is a non-water soluble source of phosphorus that must be converted to plant-available phosphate through chemical and biological processes in soil.