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Figure F9. Sedimentary rock fragments: cherts and other microcrystalline quartz. A, B. Fine grained. C, D. Well-rounded grain, potentially formed within a vesicle of a volcanic rock fragment (Fig. F15E–F15F). While not strictly sedimentary, this grain is interpreted to have formed through water-rock interaction similar in nature to diagenesis. E, F. Oversized grain with fractures filled with microcrystalline quartz. Left = plane-polarized light, right = cross-polarized light.

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