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Gemstone Info
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Tourmalines may
well claim to be the most colourful group of
gemstones. They come in any colour variation, from
green, red, blue to yellow, colourless and even black
or multi-coloured. They are thus second to no other
gemstone group concerning their wide range of colours,
however, not all these colours are equally frequent or
even equally known. The best known specimen from the
Tourmaline group are the green Tourmaline (Verdelite)
and the pink or red Rubellite. True blue tourmalines (Indigolite)
are scarce indeed, since most of the blue specimen
show a more or less clearly pronounced shade of green.
(© ICA)
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TOURMALINE
The tourmaline group has a general formula of
- AX3Y6(BO3)3
Si6O18(O, OH, F)4
The A can be either calcium or sodium. The X
can be either aluminum, iron, lithium or magnesium. The Y
is usually aluminum, but can also be chromium or iron.
Some potassium can be in the A position, some
manganese can be in the X position and some
vanadium can be found in the Y position, but these
elements are usually not represented in the formulas of
the tourmaline members.
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