Quartz (19th century)

specimen number:
1052831

location:
Rio Grande do Sul, Brazil

description:

Lustrous crystals of red quartz crystals to 2.0 cm in size covering matrix. Minimal damage present. Very neat 19th century example for this Brazilian classic. The specimen comes with an antique label as shown at the end of the video. Previously from the collection of Wilhelm Hoyer.

The amethyst deposits of Rio Grande do Sul, located in the northern southernmost province of Brazil, became a major source of global gemstone wealth during the nineteenth century. Geologically, these vast deposits are hosted within the Lower Cretaceous Serra Geral Formation, which consists of massive tholeiitic basalt flows that form part of the Parana Basin. The amethyst occurs inside large, gas-formed vesicular cavities or geodes within the basaltic host rock, where cooling lavas left hollow voids that were later filled by low-temperature, silica-rich hydrothermal fluids depositing layers of agate, chalcedony, and quartz crystals. Commercial discovery and exploitation began around 1827 when German immigrants found abundant loose geodes weathered out of the basalt in the stream beds and surface soils near Santa Cruz and Sao Gabriel. By the 1830s and 1840s, organized surface quarrying and open-pit mining operations expanded rapidly, establishing a robust export trade that shipped tons of the mineral specimens downriver to Porto Alegre for transport to cutting centers in Idar-Oberstein, Germany, a historical supply line that continued uninterrupted through the remainder of the century.

Wilhelm Hoyer was an influential nineteenth-century German mineral collector, field geologist, and civil engineer who specialized in documenting the regional mineralogy of the Saar-Nahe region and adjacent territories. Throughout the mid-to-late 1800s, he built a systematic research collection by acquiring exceptional specimens directly from active railway cuttings, infrastructure projects, and local mining adits, with a strong focus on the diverse agates, jaspers, and iron minerals native to the southwest German volcanic fields. Following his death in 1893, his extensive, well-documented mineralogical holdings transitioned into major European institutional collections and regional university repositories, serving as an important permanent scientific record of historic European mining localities.

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