The Very Highest Quality Andalusite Information...

Andalusite Back to A - Z IndexChard 24 Carat Home Page
Cushion Shaped Andalusite
Cushion Shaped Andalusite

Andalusite

General
Andalusite is an attractive and unusual gemstone, first discovered in Andalucia, Southern Spain, after which it is named. It has some similarities with the very rare and valuable alexandrite, as it is strongly pleochroic, about which more later. It is suitable for use in jewellery as it is quite hard. The fact that it is seldom seen in jewellery is probably because it is quite rare, and most people, even in the jewellery industry, have never heard of it, let alone seen it. Strangely enough, some years ago we had just finished making a ring set with a central andalusite, when another local jeweller visited us. I am sure he will not mind me identifying him as Russell Fielding. I showed him the ring, and fully expected him not to know what the stone was, when he floored and impressed me by saying without any hesitation that it looked like andalusite.

Colour
Many andalusites display different colours within the same stone. This is due to its pleochroism, which we will now explain by quoting from Robert Webster's "Gemmologists' Compendium":-

Pleochroism
The differential selective absorption of the ordinary ray and the extraordinary ray in uniaxial stones (dichroism), or of the three rays corresponding to the three principal vibration directions in biaxial stones (trichroism).
Of course, to the non-gemmologist, this explanation probably creates more confusion than clarification. It relates to the way light is refracted when passing through a stone.
Interestingly, "An Illustrated Dictionary of Jewellery" by Harold Newman describes andalusite as having strong dichroism, which is clearly incorrect as andalusite is biaxial not uniaxial, and therefore must be trichroic not dichroic. Although we find Newman's book useful, it contains numerous errors and omissions.
Typical colours for andalusite are green, brown, red, greenish-brown, brownish-green. Its pleochroic colours are red, green and yellow.
Because of the pleochroism, the colour of an andalusite can be affected considerably by the direction in which it is cut.
Our photograph is disappointing and deceptive. The actual stone is a pleasant greenish brown to red. We used flash lighting with a digital camera, followed by software adjustment of the lighting levels, and the effect was to make the stone appear quite a dull brownish colour. Who said the camera never lies?

Star Andalusite or Chiastolite
An impure variety of andalusite known as chiastolite contains carbonaceous inclusions in a cruciform arrangement. These are cut and polished for use as amulets in many countries, largely because of the symbolism of the cross.

Sources
Although as we have already noted, andalusite was originally discovered in Andalucia, it is also found in Brazil, Sri Lanka (Ceylon), Siberia, Brittany, Australia and the USA. Small non-gem crystals are also found in Cumbria, UK.

Technical Information
Chemical Composition and NameAluminium Silicate Al 2SiO5 *
Hardness7.5
Refractive Index1.634 - 1.640 to 1.644 - 1.648
Bi-refringence0.007 to 0.011
Optic SignNegative
Optical CharacterBiaxial
Specific Gravity3.1 to 3.2

Notes
* This chemical composition means that andalusite is dimorphous (has the same chemical composition) with kyanite and fibrolite.

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