Quartz

Unknown Owner

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A large attractive cut and polished slab of agate.Rio Grande do Sul, located in southern Brazil, is one of the most prolific and famous agate-producing regions in the world, centered largely around the municipality of Salto do Jacui. Geologically, these agates form within the extensive Serra Geral Formation, which consists of massive Cretaceous flood basalts erupted approximately 130 to 135 million years ago during the opening of the South Atlantic Ocean. Mineralogically, the deposits feature chalcedony, quartz, and amethyst geodes that crystallized from silica-rich hydrothermal fluids filling gas cavities and vesicles within the cooling volcanic lava flows. Historically, commercial extraction and lapidary industries began to flourish in the region during the mid-20th century, transforming local mining and processing into a major global supplier of polished geodes, mineral specimens, and decorative gemstone products.