The Algerian RPR (often named after the name of the nearest village, Djelbel Onk) has been rated as a “highly reactive phosphate rock suitable for direct application” by the world’s foremost authority on the use of various phosphate rocks as P fertilisers directly, the International Fertilizer Development Center (IFDC) in Muscle Shoals, Alabama, USA.
The IFDC are the experts in assessing the geological and geochemical make-up of phosphate rocks. This assessment is necessary to determine whether a phosphate rock is an RPR or not. The IFDC state that there is no simple laboratory solubility test that can automatically assess whether a phosphate rock is a true RPR or not. In particular, the presence of even small percentages of free lime or dolomite in a sample of a true RPR can give an artificially low ‘solubility’ in some tests, and caution is required in interpreting such analytical results.