Precious Opal from Pedro II, Brazil
Prime Gems, Inc. (New York City) offered a small quantity of precious opal from Brazil at this year’s GJX show. As an opal source, Brazil has been underrepresented for the past four decades since a “golden age” from the 1960s to mid-1970s. The inventory of Brazilian opal from Prime Gems helped inform attendees of the fine quality available from this part of the world.
Multiple states in Brazil have opal occurrences, but the most important reserves are in the Pedro II municipality, located in the northeastern state of Piauí (figure 1). According to the local artisanal miners, the first precious opals were found near the end of the 1930s. During its peak in the 1960s and 1970s, more than 30 mining operations were active. However, by the early 1980s, over two-thirds of the mines were abandoned. Currently, opal mining in this area is still small-scale and mostly manual.
The opals in this region are found in both primary and alluvial deposits. In the primary deposits, opal occurs in veins in the host sandstones (figure 2, left). This occurrence is similar to Australian opal deposits in that both are of a sedimentary nature. The vendor displayed an interesting rough opal attached to a piece of intrusive igneous rock, creating a “salt and pepper” appearance (figure 2, right). According to the vendor, diabase dikes intruded into the sedimentary rocks in this area. Diabase is of basaltic composition, and its main constituent minerals are plagioclase feldspar and pyroxene, which are of lighter and darker colors, respectively. This rough piece shows that opal also develops at the contact between the dike and the host sedimentary rocks.
At the region’s alluvial deposits, miners wash and manually extract opal. This is hard work but feasible for those who cannot afford mechanical equipment. Most of the miners alternate between opal mining during the dry summer and farming in the rainy season.
Prime Gems offered Brazilian opal with transparent light gray to white bodycolor from Pedro II, similar in appearance to white opal from Australia (figure 3, left). The play-of-color was especially charming in less transparent pieces that showed colors of the whole spectrum, with bluish and greenish colors most commonly displayed. Red play-of-color is rarer and more sought after, with a higher price tag. Some pieces with darker bodycolor resembled Australian black opal (figure 3, right).
Finished products available at the show included loose opal as cabochons, freeform polished singles or pairs, doublets, and some mosaic pieces. The top-quality materials displayed a vibrant whole-spectrum play-of-color. Opal that was of good quality but too thin for freeform single pieces was used to make doublets, with the thin opal layer glued to a dark base. To support local communities, mine operators allow the local people to use very small pieces of opal from mine waste to create mosaics for sale. The supplemental income from the sales of the mosaics can reach as much as $30 per day.
The miners informed the author that Brazilian opals are sometimes sold as Australian in the marketplace. Brazilians are proud of the quality of their opal, and opal from Pedro II is one of the two products from the state of Piauí that bear the Geographical Indication certificate. The Brazilian government grants this GI label to products or services that are characteristic of a region. The aim is to ensure that Brazilian opal is properly represented and can generate revenue to further support mining and the local communities.
