Green Tourmaline (Verdelite)

Hardness: 7-7.5 on Mohs scale. Color: Various shades of green, from light to dark, olive, bluish-green. Luster: Vitreous (glassy) to resinous. Crystal structure: Trigonal; typically forms prismatic crystals with vertical striations. Cleavage: Poor to indistinct. Specific Gravity: 3.0-3.25.

Formed in igneous and metamorphic rocks, particularly in granite pegmatites and metamorphic schists and gneisses, as well as hydrothermal veins. Its formation is associated with the interaction of boron-rich fluids with host rocks under varying pressure and temperature conditions. Geological age varies widely depending on the specific deposit, ranging from hundreds of millions to billions of years.

Primarily used as a gemstone in jewelry due to its attractive color, durability, and vitreous luster. High-quality green tourmalines are highly sought after. It occasionally finds use in specialized electrical applications due to its pyroelectric and piezoelectric properties, though this is less common for green varieties.

Green tourmaline, also known as Verdelite, is one of the most common and prized colors of the tourmaline group. The color is often due to the presence of iron, and sometimes chromium or vanadium. It is known for its pleochroism, meaning it can show different colors when viewed from different angles. Some tourmalines exhibit chatoyancy (cat's eye effect) when cut as cabochons, though this is less common in pure green varieties.

In the field, tourmaline can be identified by its distinctive trigonal crystal habit, often showing a rounded triangular cross-section, and a vitreous luster. Its hardness (7-7.5) means it can scratch glass and steel. Green tourmaline is commonly found in Brazil (Minas Gerais), Afghanistan, Pakistan, Mozambique, Namibia, Nigeria, Tanzania, and the United States (Maine, California). For collectors, identifying its strong pleochroism and its characteristic striations on crystal faces can be helpful. The specific shade of green can also be a clue to its origin.