الفهرس 
Geology and lithostratigraphyOnly 14 pages are availabe for public view
 |  | from | 201 |  |  |
| | | from | 201 | | |
Abstract
Sedimentary phosphate rocks are of an economic importance and have high tonnage and volume of world trade between 80 and 90% of phosphates, which are mainly used as a fertilizer. Phosphatic rocks are considered as one of the essential supports in the mining activity in Egypt. Phosphorite occurrences are wide spread in Safaga, Qusseir, Sebayia, Dakhla, Kharga and also in Sinai. Phosphorites are defined as sedimentary rocks which contain more thane 18-20% P205 (Tucker, 1981).Phosphorus is widespread in phytoplankton and bacteria and commonly occurs in bones, teeth and in some invertebrate shells as dahllite [carbonatehydroxylapatite- Ca,0(P04C03) (OH), (OH,F), ] (Tucker, 1981). On the death of the organisms this unstable chemical complex alters in marine waters into the more stable apatite. Francolite (carbonate fluorapatite-Ca,, Na Mg (PO,), (CO,)F) is the dominant mineral in phosphorites. Phosphates commonly contain relatively high concentrations of useful elements such as uranium, fluorine and vanadium. Phosphorus is one of the essential elements for life and is present in all living matter. Although only forming a minor part of plants and animals soft parts, phosphate is the major constituent of all vertebrate skeletons (Tucker, 1981). Both francolite and dahllite are optically anisotropic whereas collophanite appears to be amorphous under the normal petrographic microscope. A characteristic feature of apatite complexes is ionic substitution in which Ca ions are substituted by rare earth’s, uranium (U4), magnesium, barium and sodium, and PO, ions are substituted by vanadium and arsenic oxide radicals (Greensmith, 1989). In the marine environment, phosphate is a primary nutrient, so that it is controlled by organic productivity. In sea water, it is mainly present as dissolved ”orthophosphate” and particulate phosphate, with the phosphate in the latter case chiefly contained within or adsorbed onto organic detritus. In , the ocean, most organic productivity utilizes dissolved ”orthophosphate” and takes places in the upper levels through phytoplankton growth. Many sedimentary rocks contain a fewcalcium phosphate percent in the form of grains of apatite, bone fragments or coprolite.