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Andalusite and Chiastolite

                   Andalusite and Chiastolite

 

What is Andalusite?

Andalusite is a rock-forming mineral that is mined for use in high-temperature refractories. Gem-quality specimens are cut into faceted gems and cabochons.
Andalusite forms during the regional metamorphism of shale. It is found in schist and gneiss at some present and ancient convergent plate boundaries where the rocks have been exposed to the temperatures and pressures needed for its formation. In these rocks, andalusite is often associated with kyanite and sillimanite.
Andalusite also forms during the contact metamorphism of argillaceous rocks. In this situation, it can form within the metamorphosed rock or in veins and cavities within the igneous rock. It can be associated with cordierite in hornfels, granite, and granitic pegmatite

 From: https://geology.com/minerals/andalusite.shtml




Andalusite is an aluminium nesosilicate mineral with the chemical formula Al₂SiO₅. This mineral was called andalousite by Delamétehrie, who thought it came from Andalusia.


Color: Black, White, Grey, Green, Yellow, Pink, Brown, Orange
Luster: Vitreous
Crystal system: Orthorhombic crystal system
Chemical formula: Al₂SiO₅
Hardness (Mohs hardness scale): 7 – 7.5
Mineral class: Andalusite
Transparency: Opaque, Transparent
 
 
 
From: Wikipedia

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