Abstract
Spherulitic dahllite structure is first once recorded microscopically by the present authors in the phosphorite rocks in Duwi Formation in Qusier–Safaga area, Red Sea. Petrographically the study dahllite in the Duwi Formation are authigenic in origin and deposited as a secondary mineral. It is subjected to the re-crystallization process that is one of diagenetic processes. It is resulting from re-crystallization of amorphous calcium carbonate–phosphate and collophane as well as by the weathering effect. Spherulitic dahllite indicated that the phosphorite rocks of the Duwi Formation seem to be subjected to the chemical weathering. Microscopically, the spherulitic dahllite occurs as colorless to pale brown color. It consists of subhedral to anhedral crystals and characteristic by plumose fibrous texture. The spherulitic dahllite structure in the phosphorite rocks at Duwi Formation—Late Cretaceous in Egypt are comparable to those at Thermopolis Formation (Upper Cretaceous), in Cody; as well as in Ishawooa, Park County, and in Big Horn County, Wyoming, United States.
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