![]() Currier attempted to purchase more material from the mine, but apparently the major seam of rainbow hematite at Andrade underlies the primary mine haul road, and excavation would have destabilized this conduit to the open pit. One guy was backing little pieces of the stuff with obsidian and selling earrings…for $90 a pair.” Fortunately, Currier had kept enough of the rainbow hematite to select higher-grade samples, and he saw brisk sales of individual pieces.īulk samples of this Brazilian rainbow hematite are still sold at major mineral and gem shows, but our discussions with dealers indicate a growing scarcity. Initially he attempted to sell the rainbow hematite “by the barrel for $3 per pound without very much luck.” At a subsequent Tucson Gem and Mineral Show, however, he “arrived to find some guy had rented a big billboard and was selling the stuff as the latest and greatest metaphysical jewelry item. Shortly after, he shipped a truckload of 55-gallon barrels filled with an estimated 15 tons of the material to the United States. According to notes he published on, Currier first visited an outcrop of what he called “color rock” from the Andrade mine in João Monlevade, Minas Gerais, Brazil, in 1991 (figure 2 Currier, 2012). Mineral dealer Rock Currier (1940–2015) was largely responsible for introducing rainbow hematite to the U.S. Rock Currier (left) and colleague survey a seam of rainbow hematite at the Andrade mine. Nevertheless, “turgite” has been retained by the mineral collecting and gem community as a catch-all term for naturally iridescent iron (hydr)oxide minerals.įigure 2. “Turgite” was discredited as a distinct mineral name in the 1920s, however, based on thermogravimetric (Posnjak and Merwin, 1919) and X-ray diffraction (Böhm, 1928 Palache et al., 1944) studies that identified such specimens as mixtures of microcrystalline hematite (Fe 2O 3) and either goethite (FeOOH) or amorphous Fe hydroxide. The latter term originated with the German mineralogist Rudolph Hermann, who coined it in 1844 to describe iron hydroxide specimens found near the Turginsk River in the Ural Mountains (Hermann, 1844). Hematite specimens that frequently display iridescence are described as “rainbow hematite” and “turgite” (figure 1). The authors propose that this periodic substructure results from arrested crystal growth by the oriented aggregation of hematite nanorods. ![]() ![]() The organized substructure is apparent on all freshly fractured surfaces, suggesting that it represents more than an exterior surface coating. The distances between adjacent parallel spindle-shaped particles within the same layer fall in the range of 280–400 nm, generating a diffraction grating for visible light. They are arranged in three orientations at 120º angles with respect to each other and stacked layer by layer to form the bulk crystal. The nanorods are 200–300 nm in length and 50–60 nm in width. The study revealed that the interference is produced by a highly periodic microstructure consisting of spindle-shaped hematite nanocrystals containing minor Al and P impurities. The authors investigated “rainbow” hematite from Minas Gerais, Brazil, using electron microscopy, atomic force microscopy, and synchrotron X-ray diffraction to determine the cause of its intense wide-angle iridescence. Rainbow hematite from the Andrade mine in João Monlevade, Minas Gerais, Brazil. Comprehensive CAD/CAM For Jewelry Certificateįigure 1.
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