Tourmaline is a complex crystalline silicate mineral known for exhibiting the widest spectrum of colors found in the gemstone world, making it highly sought after by collectors and jewelers. Its impressive range of hues, from deep reds and blues to vibrant greens, is due to the incorporation of trace elements like iron, manganese, chromium, and copper. Trace amounts of copper are responsible for the intense neon colors of the highly prized Paraíba variety. Tourmaline also possesses pyroelectricity, meaning it can generate a weak electrical charge when heated or rubbed.
Geological Environments Where Tourmaline Forms
The formation of gem-quality tourmaline is intrinsically linked to granitic pegmatites. These rocks represent the final, water-rich stage of a cooling magma body, typically associated with granite intrusions. As the magma crystallizes into granite, incompatible elements and volatile components (such as water, fluorine, lithium, and Boron) become highly concentrated in the residual fluid.
This superheated, element-rich fluid then intrudes into fractures in the surrounding rock, forming pegmatite veins. Slow cooling, combined with volatile compounds that lower the crystallization temperature, allows for the growth of unusually large, well-formed crystals, including the transparent elbaite variety. Boron is necessary for the creation of any tourmaline mineral, making these unique magmatic-hydrothermal systems the primary source for the world’s most valuable specimens.
Tourmaline can also be found in other geological settings, though these rarely produce the quality and clarity required for faceting. Magnesium-rich dravite tourmaline, for example, is commonly restricted to metamorphic rocks, such as schists and marbles, where it forms through the recrystallization of existing boron-bearing sediments. Black, iron-rich schorl is the most common variety globally and occurs widely as an accessory mineral in granites, gneisses, and schists, often in small, opaque grains.
Major Global Sources of Gem-Quality Tourmaline
Brazil has historically been the most significant global source for gem-quality tourmaline, with mining efforts centered primarily in the states of Minas Gerais and Paraíba. Minas Gerais is renowned for producing a wide array of colors, including fine pinks, greens, and multi-colored crystals, which are frequently used in high-end jewelry. The state of Paraíba became instantly famous following the 1987 discovery of an electric neon-blue to green tourmaline, colored by trace amounts of copper, which commands the highest prices per carat in the market.
Africa has emerged as a powerhouse in tourmaline production, yielding material that rivals Brazilian finds. Deposits in Mozambique have produced copper-bearing elbaite with colors similar to the original Paraíba material, often with fewer inclusions and in larger sizes. Nigeria is a notable source for fine rubellite (red/pink) and blue-green tourmaline, as well as distinct bicolour and watermelon crystals.
Other African nations, including Tanzania, Madagascar, and Namibia, contribute a variety of colors, such as the vibrant emerald-like chrome tourmaline. The rugged mountain ranges of Pakistan and Afghanistan are well-known for yielding fine specimens of pink, red, and green tourmaline. These Asian sources provide high-quality crystals, though the challenging terrain can make mining operations sporadic.
Specific North American Localities and Unique Finds
The United States has a long and notable history of tourmaline production, particularly in the northeastern and southwestern regions. The first major gem tourmaline discovery in North America occurred in 1820 at Mount Mica in Paris, Maine. Mount Mica, along with other sites like the Dunton Mine in Newry, established Maine’s reputation for producing fine pink and green tourmaline.
The Dunton Mine gained fame for a spectacular find in 1972 and is known for the iconic “watermelon” tourmaline. This variety features a pink or red core surrounded by a green rind, perfectly mimicking the fruit from which it takes its name. Maine’s crystals have been prized for their clarity and rich colors, which have historically rivaled those found in Brazil and California.
California’s primary tourmaline deposits are concentrated in the Pala District of San Diego County, including the famous Mesa Grande and Himalaya Mines. These mines were significant producers in the early 1900s, known for their abundant production of fine rubellite (pink/red) tourmaline. The Himalaya Mine, in particular, supplied vast quantities of pink tourmaline to China, where it was highly favored by the Empress Dowager Cixi.