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Tourmaline Gemstone Information

Tourmaline is derived from the Sinhalese word Turamali meaning 'stone with mixed colours' or 'mixed parcel' probably with reference to particoloured and multicoloured stones. Those that have two colours (particoloured) and three or more colours (multicoloured). For example, Watermelon Tourmaline crystals may be pink at one end and green at the other, or pink in the middle of the crystal and green on the outside.

Tourmaline also occurs in single colours of all variations, often with excellent saturation. It has good durability and is a very popular gemstone for jewellery making. The stone shown above is a deep pink variety.

Tourmaline is a group of minerals, with complex chemical formulae, varieties include:

Rubellite: A red stone, similar in colour to ruby, some may have a violet tint. Fine stones can fetch high prices.

Pink Tourmaline: A richly coloured pink variety; it is often difficult to distinguish strong pink stones from rubellite.

Green Tourmaline: Known as verdelite, it is quite common and reasonably priced, where lithium is responsible for the colour.

Chrome tourmaline; Is also a green stone, but with a highly saturated green colour due to the presence of chromium and vanadium. Unlike verdelite, it is rare and highly priced.

Indicolite: A blue variety.

Dravite: A yellow to brown variety coloured by magnesium. Dravite is sold as a healing crystal with claims that it instils calmness and help with relaxation.

Schlor: A black variety coloured by iron and common to many parts of the world. It is sold as a healing crystal to ward off negativity with claims of other positive attributes. The crystals are mostly well formed three-sided or six-sided complete specimens.

Paraiba Tourmaline: A light blue stone coloured by copper (cupriferous) named after the Brazilian state of Paraiba, where it was first mined. It is a rare and well sort after gemstone, highly saturated stones are the most valuable of all tourmalines.

Cat's Eye Tourmaline: These stones are included with long parallel fibrous tubes that display a cat's eye effect (chatoyancy) when the stone is cut cut en cabochon. During the cutting stage, the stone must be oriented correctly (with the parallel fibres perpendicular to the base of the stone) for the effect to occur.

Colour Change Tourmaline: This variety is coloured green in sunlight (daylight) and red in incandescent light (form a filament light bulb). The colour change is distinct with well saturated, bright colours seen in high grade stones.

Source locations for tourmaline include:
Afghanistan, Africa (Malawi, Namibia, Tanzania, Zaire, Zambia, Zimbabwe), Brazil (Minas Gerais, Paraiba), India, Europe (Italy, Switzerland), Madagascar, Myanmar, Pakistan, Sri Lanka, Russia and the USA (California, Maine).

Physical Properties

Stone type:
Complex borosilicate of aluminium, magnesium, iron, calcium and alkali elements.
Crystal System:
Trigonal, occurring in long prisms that may have three, six or nine sides. The prism sides are often rounded.
Chemical Composition:
The chemical composition changes between Varieties.
Colour:
Tourmaline occurs in all colours, also parti-coloured (watermelon tourmaline) and multicoloured. Chrome tourmaline has a deeply staturated rich green colour, coloured by chromium.
Lustre:
Vitreous.
Pleochroism:
Strong in most stones showing a variation in colour depth, but absent in others.
Dispersion:
Low.
Hardness:
7 to 7½ on the Mohs' scale of hardness.
Toughness:
Good, but thermal shock 'sudden temperature change' may fracture a stone.
Cleavage:
Very uneven.
Density in gm/cc:
3.0 to 3.1
Double refraction:
Yes.
Refractive index:
1.62 to 1.64

Common Treatments

Tourmaline may be heat-treated or irradiated to improve the colour. Prolonged exposure to heat or strong light may fade the stone back to it's original colour.


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