Watermelon tourmaline is a lithium-rich variety of the mineral elbaite, named for its distinct appearance mirroring the fruit. It features a bright pink or red core surrounded by a green outer rim. This natural concentric color zoning makes it a highly sought-after material for jewelry designs.
The Geological Environment Required for Formation
The formation of this gem requires a specific and relatively rare geological setting involving lithium-rich granite pegmatites. Pegmatites are coarse-grained igneous rocks that crystallize from the final, water-rich melts of magma deep within the Earth’s crust. The residual fluid from this slow-cooling process concentrates rare elements, including lithium, boron, and manganese, which are necessary to form elbaite tourmaline crystals.
The color zoning (pink center and green rim) records the changing chemical environment during the crystal’s growth. The pink or red core forms first due to the initial presence of manganese in the mineralizing fluid. As the crystal grows, the concentration of trace elements shifts, making iron, chromium, or vanadium more available. This chemical fluctuation causes subsequent layers to crystallize with a green hue. A thin, sometimes colorless, band between the pink and green layers marks an abrupt transitional phase in the elemental composition of the hydrothermal solution.
Major Global Sources of Watermelon Tourmaline
Historically, major sources of gem-quality watermelon tourmaline have been concentrated in a few key regions. Brazil, particularly the state of Minas Gerais, remains the most notable source, producing a vast amount of the world’s supply. The pegmatite mines there are renowned for yielding specimens with exceptional clarity and vibrant color saturation, often setting the benchmark for quality.
The United States has also been a major historical source, with discoveries in both Maine and California. Watermelon tourmaline was first officially discovered in the U.S. at the Dunton Quarry in Newry, Maine, in 1902. California’s sources, primarily in the Pala and Mesa Grande districts of San Diego County, have produced some of the finest mineral specimens. The historic Himalaya Mine in the Mesa Grande district was one of North America’s largest producers of gem-grade tourmaline throughout the 20th century.
Secondary and Emerging Production Regions
Several other regions contribute significantly to the global market. Countries in Africa, such as Nigeria and Mozambique, are notable secondary producers of fine watermelon tourmaline. Nigerian deposits are known for yielding material with saturated and vivid color contrasts, adding diversity to the market supply.
Madagascar is another important source, known for producing high-quality specimens that often exhibit strong color contrasts. Asian sources, including Afghanistan and Pakistan, supply beautiful bi-color and polychrome tourmalines, though extraction in these mountainous regions can present logistical challenges.