Tourmaline

Tourmaline has captivated cultures for centuries, prized for its rainbow of colors and believed metaphysical properties. In ancient and modern lore, it is associated with protection, creativity, and emotional healing. Watermelon tourmaline, in particular, is celebrated for its vibrant color zoning and symbolic resonance. The mineral's presence in royal jewelry, art, and spiritual practices underscores its enduring allure across continents and eras.

• Tourmaline crystals can display multiple colors in a single specimen, with watermelon tourmaline showing a pink core surrounded by green.
• It is one of the few minerals that exhibits strong pleochroism, meaning its color changes depending on the viewing angle.
• Tourmaline is naturally piezoelectric, generating an electric charge when compressed or heated.
• The mineral is found on every continent, with Brazil, Afghanistan, and Madagascar among the most famous sources.
• Historically, tourmaline was often mistaken for other gemstones, leading to its name meaning "mixed gems."

Tourmaline's general chemical formula is XY₃Z₆(T₆O₁₈)(BO₃)₃V₃W, reflecting its status as a complex borosilicate. The X, Y, Z, T, V, and W positions are occupied by a variety of cations and anions, resulting in a rich diversity of species. Common endmembers include schorl (NaFe₃Al₆...), elbaite (Na(Li₁.₅Al₁.₅)Al₆...), and dravite (NaMg₃Al₆...). Boron, silicon, and aluminum are always present, with sodium, iron, lithium, magnesium, and other elements varying by species.

Tourmaline crystallizes in the hexagonal (trigonal subsystem) crystal system, specifically space group R3m. Its structure features six-membered silicate rings (cyclosilicate), which contribute to the mineral's prismatic habit and vertical striations. The arrangement of cations and anions within these rings allows for extensive chemical substitution, underpinning the group's compositional diversity and color range.

• Hardness: Mohs 7–7.5, making tourmaline durable for jewelry and handling.
• Color: Exceptionally variable—black, green, pink, red, blue, brown, colorless, and multicolored.
• Luster: Vitreous (glassy).
• Transparency: Transparent to opaque.
• Streak: White.
• Cleavage: Indistinct; fracture is uneven to conchoidal.
• Specific Gravity: 2.9–3.3, depending on species.
• Pleochroism: Strong; color intensity changes with orientation.

Tourmaline is primarily found in granitic pegmatites, metamorphic rocks such as schists and marbles, and in alluvial deposits. It often occurs alongside quartz, feldspar, mica, and other boron-rich minerals. Notable localities include Minas Gerais in Brazil, Afghanistan, Madagascar, California and Maine in the United States, and Sri Lanka. Its presence is a key indicator in geological exploration for boron and lithium-rich environments.

• Recognized Varieties: Schorl (black), Elbaite (colored gem), Dravite (brown), Uvite, Rubellite (red/pink), Indicolite (blue), Verdelite (green), Achroite (colorless), Watermelon tourmaline (pink-green zoned), Paraíba tourmaline (copper-bearing, vivid blue-green).
• Synonyms and Regional Names: Turmali (Sri Lanka), Paraíba tourmaline (Brazil).

• Gemstone: Elbaite and its colored varieties are highly sought after in fine jewelry.
• Piezoelectric Devices: Tourmaline crystals are used in scientific instruments and pressure gauges due to their ability to generate electrical charge under stress.
• Indicator Mineral: Geologists use tourmaline to locate boron and lithium deposits, aiding mineral exploration.

• Look for elongated, vertically striated prismatic crystals with a glassy luster.
• Check for strong pleochroism—hold the specimen at different angles to observe color changes.
• Note the wide range of colors, including multicolored zoning (especially in watermelon tourmaline).
• Cleavage is indistinct, and the fracture is typically uneven or conchoidal.

• Store tourmaline specimens separately to avoid scratches, as their hardness can damage softer minerals.
• Clean gently with lukewarm water and a soft brush; avoid harsh chemicals and ultrasonic cleaners.
• Protect from sudden temperature changes, which may cause fractures in some varieties.
• Handle with care, especially for elongated crystals, to prevent chipping or breakage.

• Watermelon Tourmaline: Iconic specimens from Brazil and Maine feature vivid pink-green color zoning.
• Paraíba Tourmaline: Rare, copper-bearing elbaite from Brazil, prized for its electric blue and green hues.
• Schorl Crystals: Large, opaque black tourmaline crystals from Namibia and Afghanistan are notable for their size and form.