Tourmaline - The modern birthstone for the month of October

There are fourteen different stones listed as birthstones for the calendar month of October, or as Sun/Star, Planetary, or Talismanic stones for the Zodiac sign of Libra or Scorpio. Birthstones for the calendar month of October are opal, tourmaline, jasper, aquamarine, coral, and beryl.

The Zodiac signs of Libra and Scorpio include eight additional stones: peridot, sapphire, lapis, agate, topaz, garnet, ruby, and amethyst.

Tourmaline is the veritable chameleon of the gemstone world. This popular stone is available  in more natural colours and tones than any other gemstone.  In addition to the stones being strongly  dichroic, (a single coloured stone will appear to have two different colours when viewed in different directions), many Tourmalines are actually zoned during grown across the crystal, and  exhibit  two or three colours in a single stone viewed on any axis.

Known for centuries in the Mediterranean countries, Tourmaline really  gained popularity when the Dutch East India Company began to import it into Europe in  the early 17th century from Ceylon. The name Tourmaline was chosen from the Singhalese word Turamali, to assist in the sale of this gem.

Tourmaline is actually the name of a group of related mineral species, although individual species names have been dropped in preference for the "global" terminology "Tourmaline".


What Causes The Colour?

As Tourmalines are part of a related family of mineral species, their basal chemical composition and trace element chemistry determine their colours. In simple terms they are best described as Aluminium Borate Silicates, of changeable composition.  Certain colours had been assigned specific names while others are merely prefixed with a colour before  the word Tourmaline.

Achroite: A colourless to near colourless variety
Dravite: A yellow brown to dark brown variety
Rubellite: Pink to red with or without a violet tint, with deep reds resembling Ruby.
Verdelite: A green variety, found in virtually all shades of green.
Chrome tourmaline: Another green variety, however this differs from Verdelite in that the colour is derived from the inclusion of trace amounts of chromium, resulting in rich Emerald green colours.
Indicolite: A blue variety, again found in almost all shades of blue.
Bi-Colour: Variations, zones and colour bands in Tourmaline are often purposefully accented with the cutting style to show bands and color zones in the gem. Occurring in uncountable colours variations, these are often seen in long acicular crystals.
Watermelon:– Bi-color Tourmalines which show a green skin and a red core
Canary: Bright yellow Tourmaline.
Paraíba: A rare blue-green Tourmaline. The causal element is copper imbibing the stone with an almost neon blue colour
Cat's Eye: Chatoyant Tourmaline in a variety of colors.
Colour - Change: Changes from green in daylight to red in incandescent light.

Other varieties may be simply sold with a color prefix, as in Pink Tourmaline, Green Tourmaline etc.

Purchasing Tourmaline

As with most coloured gemstones  an intense, saturated colour is the most desirable. Again personal preference dictating the colour a buyer will finally choose. In some cases the saturation of the colour can reach such a level that the stones appear almost black, as in some examples of larger Green Tourmaline. These should be avoided.

Tourmaline exhibits strong pleochroism, actually being dichroic, with two distinct colours. In either natural or artificial light these different colours or different shades of one colour  are similarly visible.

Different varieties of tourmaline tend to have differing clarities. Thus while large clean tourmalines in the blue and blue-green colors are common, almost all red and pink tourmalines will show inclusions of some kind. The most common inclusions are needles, fractures and  healed fractures.

While Tourmaline are cut in virtually any cut imaginable, the stones strong pleochroism must be considered. Tourmaline is commonly cut parallel to the longest axis of the rough crystal, in rectangles and rectangular emerald cuts (in both step and princess patterns). In this orientation darker Tourmalines exhibit the lighter of the pleochroic colors, which makes for a more pleasing stone.

Lighter Tourmalines are typically cut across the longest axis of the rough crystal, such that the table in the finished stone is parallel to the shortest axis of the crystal. This ensure that the darker of the pleochroic colours is seen when  the stone is viewed from the top.

Cabochon cut although common tend to be reserved for examples of lower clarity material.

Mineable Deposits
While Tourmaline deposits are found the world over, the most productive mines are found in Sri Lanka, Madagascar and Brazil. Lesser deposits occur in Mozambique, Zaire, Australia, Myanmar, India, Zimbabwe, Namibia, Tanzania, Thailand, Russia and the United States.

Tourmaline beach cliffs in the United States

Common Treatments
The heat treatment of Tourmaline is commonplace. Heating between 450-650 degrees Celsius produces subtle colour changes, which enhance the appearance and value of the stone. Indifferently coloured greens can become rich emerald greens, pale Paraiba and other Blue Tourmalines also benefit from heat treatment to deepen and intensify the colour.

Important & Famous Tourmalines
The Empress Dowager Tz’u His, the last Empress of China, was so taken by Tourmaline that it is rumoured she purchased nearly a ton of it for her personal collation.

The Legend
More of an interesting fact than a legend is Tourmalines ability to become electrically charged. A small electrical current can be induced in the stone, by heating, cooling or applying pressure. All three of these can be achieved by simply rubbing the stones, and accounts for the stone being known as Aschentrekker (Ash Puller) in the days of Meerschaum tobacco pipes.

Taken from Touchstone Gems www.touchstonegems.co.za 
and http://www.bernardine.com