Since at least December 2017, a photograph of an impressively tall geode has bounced around the blogophere, almost always credited to a company called Nowar Minerals Inc. and accompanied by the description “These huge Amethyst Geodes were found recently in the Santa Rosa Mining District, Artigas, Uruguay”:
We repeatedly tried to contact Nowar, which appears to be (or to have once been) an online shop that sells Uruguayan geodes, to verify the authenticity of the photograph but were unsuccessful in doing so. Although the pictured geode may be an impressive specimen, we have no reason to doubt its authenticity, as miners from the region tell us it is consistent with other locally sourced geodes, and the Artigas region in Uruguay is famous for producing impressively large amethyst geodes.
Geodes are broadly defined as hollow rocks with inward-facing crystals that form via a number of different processes generally involving the slow flow of mineral material into a pockets of air within rocks. In the case of the geodes from the Artigas region, scientists believe they were formed as mineral-laden artesian water percolated through bubbles trapped in 100-million-year old lava flows:
The amethyst-bearing geodes found in the flood basalts of the Arapey formation at Artigas (Uruguay) were formed as protogeodes by bubbles of CO2-rich basalt-derived fluids. The formation of the celadonite rim and the lining of the geodes by agate followed by quartz and amethyst were driven by the artesian water of the Guaraní aquifer percolating the basalts from below.
A May 2009 paper published in the International Journal of Earth Sciences described the Artigas region as one of the most important for amethyst mineralization and geode mining. (Amethysts are quartz-like, silica-rich crystals tinted purple by a variety of geologic processes.) In a 5 December 2018 Instagram post, Nowar Mineral’s Instagram account described the rock in question as “22 feet tall” and weighing a “mind-boggling 26,000 lbs.”
A 26,000-pound amethyst geode would not be without precedent, either: According to the Guinness Book of World Records, the largest amethyst geode (just shy of 10 feet tall) weighs 28,660 pounds. We reached out to an unrelated geode-mining company in Artigas, UruguayMinerals.com to ask if the pictured specimen was likely to have come from the Santa Rosa mining region. In response, owner Marcos Lorenzelli told us he had no doubt about its provenance: “These pieces are not from our mine, but I can assure you that they are from the mines here in Artigas, Uruguay,” he told us via email.