LOT 10.80 ct 20 pcs TANZANITE – TANZANIA

Tanzanite

Tanzanite is a gemstone that represents one of the most exciting geological “accidents” in history. A blue-violet variety of the mineral Zoisite, it is found in only one place on Earth—a small strip of land at the foothills of Mount Kilimanjaro. I have always been moved by its unique trichroism; as you rotate a fine crystal, it shifts between deep sapphire blue, royal violet, and a rich burgundy red. It is a stone of singular beauty and extreme rarity, appearing on the market only a few decades ago and quickly becoming one of the most coveted gems in the world. For the collector, Tanzanite is a “generational” treasure, born from the intense heat of tectonic shifts and finished with a color that seems to capture the very soul of the African sky.

The Heritage & Discovery

Historical Significance: Tanzanite is a modern legend. Historically, it was unknown to the world until 1967, when Maasai tribesmen discovered sparkling blue crystals on the ground that had been uncovered by a grass fire. It was originally mistaken for Sapphire, but its unique properties soon revealed it to be something entirely new. It was Tiffany & Co. that gave the stone its name, honoring its country of origin and launching it into the global spotlight. In the world of fine gems, it represents the “diamond” of the 20th century, standing as a testament to the fact that the Earth still holds spectacular, undiscovered secrets in its ancient strata.

Discovery: The first official claim was filed by Manuel de Souza, a tailor and part-time gold prospector, who initially thought he had found a massive deposit of Olivine or Sapphire. Scientifically, it is a calcium aluminum silicate. Its discovery changed the economy of the region and provided mineralogists with a new understanding of how “metasomatic” processes can produce world-class color in the presence of Vanadium.

Important Mines: There is only one source in the world: the Merelani Hills near Arusha, Tanzania. The mining area is divided into four blocks (A, B, C, and D), with Block D being legendary for producing the most intense, “AAA” grade saturation. Because the deposit is so geographically limited—roughly 7 kilometers long—it is considered “geologically finite,” meaning that within a generation, the primary source may be exhausted. For the vault, I prioritize stones with a deep, “velvety” saturation that balances the blue and violet perfectly, as these represent the absolute pinnacle of the find.

Mineralogical Profile

Description: Tanzanite is a vanadium-bearing variety of Zoisite that crystallizes in the orthorhombic system. It sits at a 6 to 7 on the Mohs scale, making it suitable for fine jewelry, though it should be treated with the care befitting a precious rarity. It is characterized by its vitreous luster and its famous pleochroism.

One of its most identifying traits is its trichroism. In its rough state, it typically shows blue, purple, and brown/burgundy colors depending on the axis of light. Most Tanzanite is gently heated to 600°C to remove the brown tones and “lock in” the spectacular blue-violet hue. It has a refractive index ($n \approx 1.69$ to $1.70$), providing a bright, crisp brilliance. Because it has one direction of perfect cleavage, it requires an expert hand during faceting to avoid “splitting” the stone on the wheel. When I facet Tanzanite, my goal is always to orient the table to maximize the “royal blue” while allowing the violet flashes to dance around the edges. It is a dense, elegant mineral that offers a depth of color that is simply unmatched by any other species.

Chemical Formula: Ca₂Al₃(SiO₄)₃(OH)