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Gem of the Month, Gemstones

Articles from GEMSTONES - LOOSE (254 Articles)












Tourmaline: a rainbow in all seasons

The name tourmaline comes from the Sinhalese word “turmali,” which means “mixed”. Colour is the major characteristic of this gorgeous stone, which is found in more hues, shades and nuances than any other gem – a veritable rainbow that really lives up to its name.

If there is a downside to the many different colours of tourmaline, however, it is that the gem struggles for its own identity and can easily be mistaken for just about any other gemstone.

Gemmologists have various names for the different colours of tourmaline, including rubellite, verdelite, indicolite, dravite, achroite, siberite, schorl and the unique liddicoateite.

Mineralogists, however, would prefer them to be called by their colour and then “elbaite”, which is the mineralogical name for tourmaline.

Tourmaline is a crystal boron silicate mineral belonging to the trigonal crystal system. It occurs as anything from long and slender to thick, prismatic and columnar crystals that are usually triangular in cross-section.

Tourmaline is a durable mineral with a hardness of seven on Moh’s scale, and boasts strong pleochroism, which means that it shows different colours, or depths of colour, when viewed at different angles or rotated in the light.

Tourmaline is found in various locations globally, including Brazil, the USA, Tanzania, Madagascar, Afghanistan, Pakistan, Sri Lanka, and Malawi.
 


If there is a downside to the many different colours of tourmaline, however, it is that the gem struggles for its own identity and can easily be mistaken for just about any other gemstone.

Gemmologists have various names for the different colours of tourmaline, including rubellite, verdelite, indicolite, dravite, achroite, siberite, schorl and the unique liddicoateite.

Mineralogists, however, would prefer them to be called by their colour and then “elbaite”, which is the mineralogical name for tourmaline.

Tourmaline is a crystal boron silicate mineral belonging to the trigonal crystal system. It occurs as anything from long and slender to thick, prismatic and columnar crystals that are usually triangular in cross-section.

Tourmaline is a durable mineral with a hardness of seven on Moh’s scale, and boasts strong pleochroism, which means that it shows different colours, or depths of colour, when viewed at different angles or rotated in the light.

Tourmaline is found in various locations globally, including Brazil, the USA, Tanzania, Madagascar, Afghanistan, Pakistan, Sri Lanka, and Malawi.
 

Rubellite

Rubellite tourmalines can, and do, vary in colour from mid to deep reds that closely resemble ruby; however, only a few of these are entitled to call themselves rubellites. The name comes from the Latin ‘rubellus’, which means reddish. Rubellite is one of the rarest and most valuable tourmalines. Many gems in the 17th-century Russian crown jewels that were originally thought to be rubies are actually rubellite tourmalines.
 

Verdelite

Verdelite is the term used by gemmologists to refer to green tourmalines and there is a broad range of shades – some are very light, while others are so dark that the green colour can only be recognised when the stone is held against the light.

Wonderful examples of verdelite tourmaline exist in the colour range between blue-green and dark bottle-green. Chrome tourmaline is green also, but is considered different from the regular greens as it derives its rich, green colour from trace elements of chromium.
 

Indicolite

Indicolite occurs in bright blue hues to bluish green colours – think indigo – and good quality stones are quite rare so specimens are regarded as highly collectable.

The blue/green tourmaline in peacock hues, from Paraiba in Brazil, certainly took the world by surprise when discovered in 1989. This tourmaline soon became known as “Paraiba” and its colours have often been described as “neon”, since they appear to glow.
 

Dravite


Dravite is found in tones of golden brown and tawny brown, and is another variation of tourmaline for which stones of good quality are not often available.

There is a new yellow tourmaline from Malawi, discovered in the autumn of 2000, that is clear and pure with just a hint of green. Under the trade name “canary”, this exciting new tourmaline variety has now begun to circulate in the marketplace.
 

Schorl

Schorl or black tourmaline is very inexpensive compared to other colours and can often be found in much larger sizes – sometimes over 70 carats! It is sold in spheres and cabochons, but the faceted pieces display the best brilliance. Tourmaline is one of the few gemstones where you can find a range of bi-colour and tri-colour specimens.

These occur in all colours, but the most coveted colour is the watermelon tourmaline, named for its distinctive pink/red centre and green outer edge. Top specimens are highly regarded by collectors and usually cut as slices. If the colour zones of the crystal lie on top of one another, the Brazilians call it a “papageios” or rainbow tourmaline.
 

Liddicoatite

Liddicoatite typically exhibits extraordinarily-beautiful, geometrically-patterned colour zoning. It was recognized as a unique mineral species in 1977, and was named in honour of American gemmologist Richard Liddicoat.

When discovered, it was the sixth tourmaline species to be recognized – today, there are 14 different tourmaline group members – and the most famous source of these remarkable polychrome tourmalines was the Anjanabonoina pegmatite district in central Madagascar.

Liddicoatite of quality is only occasionally available, most commonly seen as polished slices that show off the characteristic zoning patterns.

China’s Dowager Empress Cixi of Qing Dynasty highly prized the pink tourmaline that was mined in Pala. Under her influence, the appetite for this gem created a boom in the California tourmaline industry that saw 120 tons of gem-grade material mined between 1902 and 1910.

Much of this found its way into the Empress’ personal coffers and she was laid to rest on a pillow of carved, pink tourmaline.

Ultimately, tourmaline is an attractive gem that stands up to its rainbow name. In fact, the term describes tourmaline so well that one could have a collection of them in every colour and feel as though one had gathered the entire world of gems.

For more information on how to learn more about tourmaline and other gems please visit http://www.gem.org.au

 

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Wednesday, 26 September, 2018 10:28am
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