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Tourmaline
Chemical Composition Complex chemical formulas containing Aluminum Borosilicates and varying quantities of sodium, magnesium, calcium, iron, chromium, manganese, potassium, etc.
Colour Extremely wide colour range.
Refractive Index R.I. 1.63-1.64, varying with the composition.
Durability Hardness 7.0-7.5.
Crystal Structure Hexagonal
Specific Gravity 3.0-3.25, varying with the composition.
Sources / Occurrence Notable deposits include California, Maine, Brazil, Namibia, Madagascar, Zambia, and Afghanistan.
Varieties

Indicolite (blue or blue-green) -- moderately scarce and expensive in fine qualities.

Rubellite (red) -- moderately scarce and expensive in fine qualities. Often badly included.

Bicolour or tricolour tourmaline -- shows multiple colour zones throughout the crystal. Highly prized when the colours are well divided and vivid. Often badly included and subject to fracture along the colour transition line.

Watermelon tourmaline -- has a red central core surrounded by green, resembling the cross section of a watermelon. Often cut in thin slices to show the colours to best advantage.

Schorl -- black tourmaline

Dravite -- brown tourmaline

Chrome tourmaline -- vivid green. Derives its colour from chromium. Appears red when viewed through a Chelsea filter (emerald filter). Fairly scarce and expensive.

Achroite -- colourless tourmaline. Fairly rare

Pink Tourmaline

Cat’sEyeTourmaline

Yellow Tourmaline

Ancient people from Ceylon called it 'Turmali', which means 'many colours' in Sinhalese. Tourmaline is the national gemstone of the U.S.

The array of colours provides a fascinating quest for the discerning seeker of nature's bounty. For several centuries Tourmaline has adorned the jewels of royalty. The Empress Dowager Tz's Hsi, the last empress of China, valued the rich pink colours of this stone above all other stones.

The stone is a powerful gem, which strengthens the body and spirit. It is also believed to be good for diabetes, syphilis and gonorrhea.

It is the birthstone for the month of October.