description Andalusite Overview
Andalusite is an aluminum silicate mineral with the chemical formula Al2SiO5. It forms in metamorphic rocks and is named after Andalusia in southern Spain. Gem-quality andalusite is valued for pleochroism, meaning that its apparent color changes when viewed from different directions. A related variety called chiastolite contains dark carbonaceous inclusions arranged in a cross-like pattern.
help Andalusite FAQ
What is andalusite made of?
Andalusite is an aluminum silicate with the chemical formula Al2SiO5. It forms in metamorphic rocks and is one of three Al2SiO5 minerals, alongside kyanite and sillimanite. [GIA](https://www.gia.edu/doc/SU09.pdf)
Why does an andalusite gem seem to change color?
Andalusite shows strong pleochroism, so its apparent green, yellow, brown, or reddish tones vary with viewing direction. This is an optical effect caused by crystal orientation, not an electronic color change.
Why is andalusite named after Andalusia?
The mineral was named after Andalusia in southern Spain, where it was first identified. Gem-quality material is also known from Brazil, Sri Lanka, Madagascar, and other countries.
What is chiastolite in relation to andalusite?
Chiastolite is a variety of andalusite with dark carbonaceous inclusions that can form a cross-shaped pattern. The pattern is visible in some polished slices and rough crystals.
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