Biogenic phosphates in some diagenetically modified sandstones are subject to pressure solution by detrital quartz and/or to replacement by silica. Silica replacement preserves the shape of the fossil, whereas pressure solution destroys the fossil and leaves a welded aggregate of quartz. In either case the resulting product is distinctive, and its recognition should enable petrographers to document the former presence of biogenic phosphates in diagenetically altered sandstone.

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