Phosphorites occur throughout the Negev, southern Israel, within the upper part of the Mishash Formation of Late Campanian age. These phosphorites are part of the Upper Cretaceous-Eocene Tethys phosphatic province. Two units can be differentiated in the Mishash Formation: a lower chert unit and an upper phosphatic unit (Nathan et al., 1979). In the upper unit, rich, economic phosphorite beds with more than 25% P2O5 alternate with chert beds and so-called ‘sterile intercalations’ which contain about 15% P2O5.
Clinoptilohte (Mumpton, 1960), a zeolite of the heulandite-clinoptilolite family, was identified from XRD patterns of air-dried and heated samples of the clay fraction from the insoluble residue (1-20% of the rock) of selected phosphatic samples from the Hor Hahar field, Negev, southern Israel. Clinoptilohte occurred mainly in the ‘sterile intercalations’. Inasmuch as clinoptilohte has not been identified in older formations in the Negev, it was presumed to be authigenic in the Mishash Formation.