Quartz var. Agate

Unknown Owner

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A cut and polished on one side slabbed of agate. This is a neat historical example dating to the 19th century. The specimen comes with a previous antique label and at one time was part of the collection of Wilhelm Hoyer.Rio Grande do Sul, the southernmost state of Brazil, is famous for its extensive deposits of agate, which are hosted within the early Cretaceous basaltic lava flows of the Parana Basin, formed roughly 130 million years ago. As the vast basalt flows cooled, escaping volcanic gases left cavities, or vesicles, in the rock. Over millions of years, silica-rich groundwater seeped into these cavities, depositing microscopic quartz crystals layer by layer from the outer walls inward, creating the characteristic banded structures. Historically, mining of these geodes began in the early nineteenth century with German immigrants, who recognized the quality of the material and began shipping it back to the lapidary cutting centers of Idar-Oberstein, Germany. Today, the Salto do Jacui region is the primary extraction hub, supplying large quantities of basalt-hosted agate to global markets for industrial, ornamental, and lapidary use.Wilhelm Hoyer (1849-1913) was a German civil engineer and mineral collector based in Hanover who utilized his professional work in railway construction and geological surveys to assemble a significant mineralogical and paleontological collection. Active during the late nineteenth and early twentieth centuries, Hoyer specialized in documenting and collecting from the Mesozoic formations of northwestern Germany, preserving regional specimens from active quarries and construction sites. His systematic approach to labeling and documenting specimens provided important historical provenance, and following his death, his comprehensive collection was integrated into major academic repositories, including the University of Gottingen and the Prussian Geological Survey in Berlin.