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Quartz crystals in iron formation (Soudan Iron-Formation, Neoarchean, ~2.722 Ga; Vermilion Iron Range, Minnesota, USA) (23141802269).jpg - Ser Amantio di Nicolao
Quartz-mineralized fault zone in slate (Biwabik Iron-Formation, Paleoproterozoic, ~1.878 Ga; Thunderbird Mine, Mesabi Iron Range, Minnesota, USA) 3 (31597451546).jpg - Rudolphous
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