Tourmaline

  

Available in all the colours of the rainbow, Tourmaline also has a very complex mineral composition, which is the main reason behind their rich colour composition. Gemstones from Sri Lanka belonging to the Tourmaline species differ from yellowish-green to bright green.

One of the most important gem Tourmalines found in Sri Lanka are mixtures of Dravite and Uvite. Often brown, yellowish-brown, reddish-brown, or nearly black in colour, these species contain traces of vanadium, chromium, or both. When present in the right concentrations, these impurities produce rich green hues similar to tsavorite garnet.

While Uvite is rich in calcium, magnesium, and aluminium and Dravite is rich in sodium, magnesium, and aluminium; both forms within limestone that have been altered by heat and pressure and are fondly known as Savanna Tourmaline by gem dealers and merchants.

• Varieties: Bi-coloured, watermelon, cat’s eye, alexandrite-like (rare).
• Sources: Sri Lanka, Brazil, USA (California, Maine), Madagascar, Tanzania, Kenya, Russia, Afghanistan, Pakistan (prime new source).
• Toughness: Tourmaline ranks 7 to 7.5 on the Mohs scale.
• Precautions: Do not store in direct sunlight. Whilst tourmaline tends to be fairly stable and isn't affected by chemical exposure, it can still be harmed in heat.
• Treatments: The two most important tourmaline treatments are heating and irradiation. Changes resulting from heat treatment are stable and undetectable. Gems with abundant liquid inclusions can't withstand heat treatment. Color changes due to irradiation can fade with exposure to heat or bright light.
• History: In the 1500s, a Spanish conquistador found green tourmaline in Brazil which he mistook for emerald. His error held until the 1800s, when mineralogists finally identified tourmaline as its own mineral species. Variations of the name “schorl” may have been used to describe black tourmaline even before 1400.