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Encyclopedia Britannica - Main :: ANC-APO |
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ANDALUSITE , a mineral
dome -faces. As a rule
kaolin
colour, occur abundantly in the mica-schist of the Lisens Alp near Innsbruck
mineral
topaz
district
Andalusite is typically a mineral of metamorphic origin, occurring most fre- quently in altered clay-slates and crystalline schists, near the junction of these with masses of intrusive igneous rocks such as granite. It has been recognized also, however, as a primary constituent of granite itself. A curious variety of andalusite known as chiastolite is specially characteristic of clay-slates near a contact with granite. The elongated prismatic crystals enclose symmetrically arranged wedges of carbonaceous material, and in cross-section show a black cross on a greyish ground. Cross-sections of such crystals are polished and worn as amulets or charms. Crystals of a size suitable for this purpose are found in Brittany and the Pyrenees, while still larger specimens have been found recently in South Australia. The name chiastolite is derived from the Greek xraoros, crossed or marked with the letter x: cross-stone and made are earlier names, the latter having been given on account of the resemblance the cross-section of the stone bears to the heraldic macula or mascle. (L. J. S.)End of Article: ANDALUSITE If you wish, you can link directly to this article.
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