The quartz of Fazenda Pacú occurs in veins which are formed along a fracture zone at the contact between granite (Archean) and argillaceous sediment (Silurian). Rock decay has decomposed the granite and altered the binding material of the quartz of the veins. Kaolinite has resulted. Erosion has removed the upper part of some veins, redepositing the crystals in boulder beds separated by sedimentary clay. The crystal-bearing veins are probably of hypogene origin and are related to a later phase of the prominent pegmatitic invasions which have occurred in Minas Geraes.

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