Rock phosphate contains about 75% tricalcium phosphate. It should not be used unless it is guaranteed to contain less than 0.5% fluorine. Rock phosphates from some areas (e.g., Curacao) are low in fluorine, whereas those from other areas must be defluorinated before they can be used. Defluorination of rock phosphate is an industrial process that is suitable only for large-scale production. Rock phosphate contains about 17% phosphorus and 34% calcium.