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Name Origin | Andalusite is named after the first noted locality, Andalusia, Spain |
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Chemical Formula | Al2SiO5 +Fe |
Color | Pinkish, reddish-brown, rose-red, whitish, grayish, yellowish, violet, greenish |
Hardness | 6.5 - 7.5 on Mohs Scale |
Crystal System | Orthorhombic, Crystals prismatic, striated, square in cross section, massive, compact |
Cleavage | Distinct 1 direction. Fracture even to sub-conchoidal. Brittke |
Spectral | Deep green varieties from Brazil display Mn spectrum: knife edge shadow at 5535, fine lines at 5505 and 5475; faint lines at 5180, 4950, and 4550. |
Specific Gravity (SG) | 3.13 - 3.17 |
Luster | Vitreous to subvitreous |
Stone size |
Gems from Brazil reach 75-100 carats. Usually gems are 1-5 carats; stones in the 5-10 carat range are available at several times the cost of the smaller ones. |
Pleochroism | Strongly pleochroic; olive green to flesh-red (Brazil) Usually yellow/green/red Blue andalusite from Belgium: Blue/colorless/colorless |
Note: Andalusite is an aluminum silicate with the formula \(Al_2SiO_5\). The color of pure andalusite is white but the presence of some impurities give it red, pink, reddish-brown, green colors. The pink and red colors are due to presence of iron and the green colors are due to the presence of manganese. The mineral has the attractive property of displaying different colors when viewed from different directions. The pleochroism is
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usually in reddish and green tints. Clear andalusite can be confused with tourmaline.
Viridine is a deep green variety containing manganese. Chiastolite (also called macle-stone or cross stone) is a variety of andalusite in which the regular arrangement of carbonaceous impurities has led to formation of a colored cross as seen in a cut transverse section of the crystal. because of impurities it contains, chiastolite has a lower hardness and density than other varieties of andalusite. The name chiastolite is from the Greek chiastos, arranged diagonally, because the pattern of carbon inclusions resembles the Greek letter Chi.
Viridine is a deep green variety containing manganese. Chiastolite (also called macle-stone or cross stone) is a variety of andalusite in which the regular arrangement of carbonaceous impurities has led to formation of a colored cross as seen in a cut transverse section of the crystal. because of impurities it contains, chiastolite has a lower hardness and density than other varieties of andalusite. The name chiastolite is from the Greek chiastos, arranged diagonally, because the pattern of carbon inclusions resembles the Greek letter Chi.
Photo Credit:
"AndalousiteTyrol" by Didier Descouens - Own work. Licensed under CC BY-SA 4.0 via Commons - https://commons.wikimedia.org/wiki/File:AndalousiteTyrol.jpg#/media/File:AndalousiteTyrol.jpg
www.shutterstone.com
"AndalousiteTyrol" by Didier Descouens - Own work. Licensed under CC BY-SA 4.0 via Commons - https://commons.wikimedia.org/wiki/File:AndalousiteTyrol.jpg#/media/File:AndalousiteTyrol.jpg
www.shutterstone.com