A detailed study of pellets has been carried out for microgranular phosphorites from the standard phosphorite-bearing basin Karatau, Kazakhstan, in order to refine ideas of genesis of this basic industrial type of phosphate ores. Large magnifications reached by means of a scanning electron microscope permitted us to see that the phosphate grains are chiefly made up of phosphatized remains of bacterial-algal mass and accumulations of microscleras of spongae (spongolites). The bacterial-algal organics in the phosphate matter is dominated by ball-, bacillus-, and cone-shaped forms. Coated grains of concentric (oolithic) structure are widespread. They may be considered oncolites, i.e. varieties of bacterial-algal and partly sponge biotas, the source for phosphate grains, which formed in other environments and in other places. The latter were much shallower than the settings where mechanical accumulation of grains proceeded and where phosphorites themselves came into existence.

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First page of ULTRAMICROSTRUCTURES OF PHOSPHATE PELLETS OF MICROGRANULAR PHOSPHORITES FROM THE STANDARD BASIN KARATAU (<italic>Kazakhstan</italic>)
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