Quartz

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An attractive cluster of gemmy mostly purple quartz crystals, this material often referred to as ametrine. a number of the faces on these crystals have been ground and polished. When backlit the yellow coloration is obvious. The Anahi mine, located in the Angel Sandoval Province of the Santa Cruz Department in eastern Bolivia, is a world-famous underground mining operation celebrated as the primary commercial source of ametrine. Geologically, the deposit is a hydrothermal fault-breccia system hosted within the Cambrian-age Murcielago Group dolomitic limestones, which were fractured during regional tectonic activity. Silica-rich hydrothermal solutions circulating through these breccias deposited quartz within open vugs and veins, with trace iron impurities and highly specific, alternating temperature zones creating the distinct color variations. Small-scale artisanal extraction of gemstones by local indigenous groups dates back centuries, but organized commercial underground operations began in 1989 when the Minerales y Metales del Oriente mining company secured the formal concession. The mine has utilized systematic shaft and gallery mining techniques to extract gem-grade quartz and fine collector specimens continuously for decades, remaining highly active well into the 2020s. Ametrine, also known commercially as bolivianite, is a rare and striking bi-color variety of quartz that displays distinct zones of purple amethyst and yellow-to-orange citrine within the same single crystal. This unique color zoning is caused by differing oxidation states of iron impurities within the crystal lattice, which are controlled by precise temperature gradients and localized geochemical variations during the crystal's growth. As the quartz prism develops, iron is incorporated into different sectors at varying valences, resulting in sharp, geometric color sectors that align perfectly with the crystal's rhombohedral faces. Because these precise geological conditions are incredibly uncommon, the sharp color-zoned crystals from the Anahi mine represent the definitive standard for this variety, making them highly prized by gem cutters and mineral collectors worldwide.