Martin Rees, Jeweller and Pawnbroker


An attractive blue-violet stone.  A complex silicate of magnesium and aluminium.

Unusual Optical Quality

We only recently had the chance to examine an unmounted stone.  The owner knew nothing about it, so we wanted to identify it for him.  We first admired its beautiful colour, then under the microscope I turned it sideways.  To my amazement the colour had vanished!  The stone now looked transparent.  And that's its strange quality, caused by its crystal structure.  At once we could identify the stone (after carefully checking it wasn't a doublet, which can sometimes produce similar effects).
The stone requires careful cutting to ensure its colour is seen when viewed from above.  Cut it badly, and it will lose its colour.

Why the Vikings prized Iolite

When boats navigate without a compass they rely on the sun.  And that can be a problem when it's cloudy.  But Iolite works like a polarising filter, so can be used to work out the sun's position.  Because light from the sky is polarised, it looks darker according to its angle from the sun.  Bees also tell the direction of the sun by using polarised light.

Caring for Iolite

It can be cracked by hard blows.  Like many semi-precious stones it will get scratched by the grit in household dust, so do not wear it when doing manual work.
Cleaning is simple.  If necessary it can withstand soaking in hot water.  It can be cleaned with jewellery cleaner.

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Cabochon Cut Iolite Above: This cabochon shaped stone is illuminated from the left (you can see the lamp reflected at the side).  From the top it's a beautiful blue/violet.  But see how the light refracted through the stone makes the right edge of the stone look white.  That's an unusual optical effect.  The bright blue area in the centre of the stone is caused by a large fracture.  Click here for larger image, 143KB

Detail of Iolite seen from the back Above: The same stone viewed from the back.  Most of the stone is visible in the larger image, but this picture just shows a small detail.  Note the triangular pattern, caused by what look like strings of bubbles in the crystal structure.  This gives the stone a very faint star, visible when viewed, but not in our pictures here.  Click here for larger image, 279KB

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