Andalusite

Andalusite is an aluminium nesosilicate mineral with the chemical formula Al2SiO5.The variety chiastolite commonly contains dark inclusions of carbon or clay which form an X or a cross in section.A clear variety first found in Andalusia, Spain can be cut into an interesting gemstone. Faceted andalusite stones give a play of red, green, and yellow colors that resembles a muted form of iridescence, although the colors are actually the result of unusually strong pleochroism.
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(n.)
A silicate of aluminium, occurring usually in thick rhombic prisms, nearly square, of a grayish or pale reddish tint. It was first discovered in Andalusia, Spain.
  

General Information:
 Chemical Formula:
Al2SiO5 = Al[6]Al[5]OSiO4
 Composition:
(Molecular Weight = 162.05 gm)
Aluminum 33.30 % Al
Silicon 17.33 % Si
Oxygen 49.37 % O 
 Empirical Formula:
Al2SiO5
 Environment:
Metamorphosed peri-aluminous sedimentary rocks.
 Locality:
Andalucia (Spain), an early but now unimportant location.
 Name Origin:
Named after its locality.
Physical Properties:
 Cleavage:
[110] Distinct, [100] Indistinct, [010] Poor
 Color:
dark green, gray, brown, red, or green.
 Density:
3.13 - 3.17, Average = 3.15
 Diaphaniety:
Transparent to translucent
 Habits:
Blocky - Crystal shape tends to be equant (e.g. feldspars)., Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline)., Euhedral Crystals - Occurs as well-formed crystals sho wing good external form.
 Hardness:
6.5-7 - Pyrite-Quartz
 Luminescence:
None.
 Luster:
Vitreous (Glassy)
 Streak:
white
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andalusite
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ANDALUSITE