|The Very Highest Quality Andalusite Information...|
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.
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":-
PleochroismOf 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.
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).
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.
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.
|Chemical Composition and Name||Aluminium Silicate Al 2SiO5 *|
|Refractive Index||1.634 - 1.640 to 1.644 - 1.648|
|Bi-refringence||0.007 to 0.011|
|Specific Gravity||3.1 to 3.2|
* This chemical composition means that andalusite is dimorphous (has the same chemical composition) with kyanite and fibrolite.
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