THE MINERAL ANDALUSITE

  • Chemistry: Al2 SiO5, Aluminum Silicate
  • Class: Silicates
  • Subclass: Nesosilicates
  • Uses: in the manufacture of spark plugs etc, as a gemstone and as mineral specimens.
  • Specimens

Andalusite is named for its type locality of Andalusia, Spain. It is a polymorph with two other minerals: kyanite and sillimanite. A polymorph is a mineral that shares the same chemistry but a different crystal structure with other minerals.

A unique variety of andalusite is called "chiastolite". It contains black or brown clay and/or carbonaceous material (often graphite) inclusions in the crystal. These inclusions are arranged in regular symmetrical shapes - especially prized when they are in the form of a cross or X.

PHYSICAL CHARACTERISTICS:

  • Color is white, red, brown, orange and green.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System is Orthorhombic; 2/m2/m2/m
  • Crystal Habits include prismatic crystals with a square cross section terminated by a pinacoid. also massive and granular.
  • Cleavage is good in two directions.
  • Fracture is splintery to subconchoidal.
  • Hardness is 7.5
  • Specific Gravity is approximately 3.15+ (above average)
  • Streak is white.
  • Associated Minerals are cordierite, biotite, feldspars, quartz, kyanite and sillimanite.
  • Other Characteristics: dark inclusions produce cruciform shapes in the variety chiastolite. Index of refraction is 1.632-1.638.
  • Notable Occurrences include Andalusia, Spain; Austria; California, USA and China.
  • Best Field Indicators are crystal habit, color, inclusions (if present) and hardness.
This Site Awarded
Available ANDALUSITE specimens:
see this List of ALL specimens including SOLD ones

 

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