While the red hues of rubellite maintain a steady appreciation, the interest and value of blue and green tourmaline was reignited with the discovery of ‘ParaÃba’ tourmaline, STACEY LIM reports.
Tourmalines showing unusually striking “neon” colours of blue, green-blue, green and violet first appeared in the jewellery trade in 1989 when a single deposit was unearthed near the Brazilian village of Sao Jose de Batalha in north-central ParaÃba State. ‘ParaÃba tourmalines’ are rare and with a vivid blue and startling glow incomparable to any other gem.
Although uncommon in sizes over 2 carats, these majestic stones are always in high demand, attracting extraordinary prices not seen with any other tourmaline variety.
Interestingly, the trace element responsible for these exciting colours is copper and in some cases the content is so high that small inclusions of pure native copper can be found. While copper is a contributing colouring agent in many other minerals such as turquoise and malachite, it has not been known to colour tourmaline until this discovery.
Typically, iron and chromium induce the blue and green in other coloured tourmaline varieties.
Mined by hand in the copper-rich mountains of Mozambique and Nigeria are ‘ParaÃba-type’ tourmalines. Almost identical in chemistry and colour saturation to their Brazilian counterparts, these gems emerged into the market in the early 2000s with large stones, some over 5 carats, however some argue the quality and richness of colour of the authentic Brazilian stones are incomparable.
In contrast to ParaÃba tourmaline, the other cool-hued varieties are more readily available and at less extravagant prices. These gems flaunt trade names such as ‘indicolite’, the name given to a range of blue tourmalines, and ‘verdelite’, the name given to a range of green tourmalines. Both named varieties are often tinged with blue, green or violet offering a broad spectrum of colours in varying saturations.
Blue tourmalines range from pale icy blue to deep and dark saturated navy blues. Pure blues are less common and stones that exhibit a dominant blue hue generally attract a higher value.
Some stones are labelled indicolite even when the green predominates, so buyers should value a stone based on its colour rather than its trade name.
Tourmaline’s other varying greens offer a pleasing alternative to the yellowy grass green of peridot and the deep, rich green of emerald, the other industry heavyweights. These include pastel hues, blue-green ‘teal’ varieties and a rare vivid green referred to as ‘chrome dravite’, coloured by vanadium, chromium and sometimes both.
Green tourmalines are commonly dark olive gemstones and not overly attractive, absorbing light so intensely they can appear almost black from some directions.
With the lighter tone viewable through the prism of a crystal, cutters typically orientate these stones with the table parallel to the prism face, offering a paler stone but showing a less attractive brown to yellowy green.
With such an extraordinary discovery like ParaÃba tourmaline in our lifetime, one wonders what else lies beneath the earth waiting to inspire the gem world and spark another love affair with a colourful gemstone.
More reading: Colour investigation: Tourmaline - Part I
Frank
No comments: