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Gem of the Month: Tourmaline

tourmaline-icga.jpgThe theme for October birthstones is colour and lots of it!  We have already covered Opal with its “play of colour” in a previous article.  This time, we look at the alternative birthstone for October: tourmaline – the Rainbow Stone.  (Photo from ICGA article)

Gemmology Matters:  Tourmaline is truly a fascinating gemstone. Tourmaline is a very complex group of minerals but may be described as a complex aluminium borosilicate where colour is caused by presence or absence of various metal ions (Fe, Mn, Cr, V, Ti and Cu) in the crystal structure.  Hardness is 7 to 7.5 on the Moh Scale making it suitable for most jewellery applications.  Commonly found as prismatic crystals (trigonal-hexagonal), often with vertical striations along the prism faces.

While it can have fantastic colour, strong dichroism and sometimes unstable crystal structure means that tourmaline can be quite challenging for the gem cutter. Cutting orientation is very important so that the faceted gem displays the best colour possible.  Where the colour is too dark looking through the crystal (referred to as “closed C-axis”), they may be cut in elongated shapes (where the A-B axis shows better colour).  Some types can be unstable during the cutting process – if not handled carefully, the stone can crack badly while being faceted.

A fascinating property of some types of tourmaline has led to it being used for scientific and industrial purposes.  The piezoelectricity effect occurs when an electrical charge is induced by applying pressure to a tourmaline crystal in the direction of the vertical crystal axis – this can be used in pressure measuring equipment and other scientific applications.  A similar effect called pyroelectricity occurs when the crystal is heated yielding a positive charge at one end of the crystal and a negative charge at the other.

Tourmalines are mined everywhere in the world with important commercial deposits located in Brazil and parts of Africa.  Other notable locations include Sri Lanka, Madagascar, Pakistan, Afghanistan and the USA. The price range for gem quality Tourmaline varies almost as much as its colour with some rare and sought after varieties bringing extremely high prices.  The recently discovered Paraiba source in Brazil with its intense neon blue coloured stones produces gems that are particularly sought after.

mixed_tourmalines.jpg325g-tourm-sm.jpgThese photos show a small selection of mixed colour tourmaline from Nigeria.  Dont have much of this material left now so keep your eye on our online shop for the last few bits.

Mythology and Lore:  Tourmaline is known as the “Rainbow Stone” from an ancient Egyptian legend: on the long way from the Earth’s heart up towards the sun, Tourmaline travelled along a rainbow, collecting all the colours of the rainbow on its journey.  The name derives from the Sinhalese (Ceylon) word “tura mali” meaning stone of mixed colours. 

The Empress Dowager Tz’u Hsi, the last Empress of China, was a great collector of pink tourmaline and rubellite.  She imported tons of tourmaline from Southern California in the early twentieth century, creating a gem rush in San Diego during the period.  She loved pink tourmaline so much that she was laid to rest on a pillow carved from this gemstone. 

Tourmaline is the birthstone for the month of October and is associated with the zodiac sign of Libra.  Legend says tourmaline inspires artistic expression, enhances intuition, increase self-confidence and amplify one’s psychic energies.  Tourmaline may be used to neutralize negative energies, dispel fear and grief, and to aid in concentration and communication.

Alternatives in Multicolour:  Tourmaline is unique for its range of colours and gems where more than one colour is displayed.  While tourmaline may be found in many colours which are also represented by other gems, it is the bi- and multi-coloured varieties which are difficult to find elsewhere in the gem world.  Sapphires may show this bi-colour character (called “parti” in Australia) but generally the colours tend toward the blue-green-yellow and do not display the sharp boundaries of significantly different colours seen in some tourmaline.

Links of Interest: 

Hope you enjoyed this article on Tourmaline – truly worthy of a book but we’ll leave that job to someone else.  We still have some nice pieces of tourmaline rough in stock as well as some nice cut gems in a variety of colours (including nice emerald greens and intense pinks). Please enquire at any time about these. 

Cheers for now from Aussie Sapphire