Andalusite

Andalusite
Andalusite
General
Category	Nesosilicates
Formula (repeatin unit)	Al2SiO5
Strunz clessification	09.AF.10
Creestal seestem	orthorhombic
Space group	2/m 2/m 2/m - Dipyramidal
Unit cell	a = 7.7980 Å b = 7.9031 Å c = 5.5566 Å; Z = 4
Identification
Colour	Pink, violet, yellae, green, white, gray; in thin section, colourless tae pink or green
Creestal habit	As euhedral crystals or columnar aggregates havin nearly square cross sections; fibrous compact tae massive
Twinnin	On {101}, rare
Cleavage	Guid on {110}, puir on {100}
Fractur	uneven tae subconchoidal
Mohs scale haurdness	6.5 - 7.5
Skinkle	Vitreous
Streak	White
Diaphaneity	Transparent tae nearly opaque wi inclusions
Speceefic gravity	3.17 (+/- .04)
Optical properties	double refractive, biaxial negative; chiastolite haes anomalous aggregate reaction.
Refractive index	nα = 1.629 - 1.640 nβ = 1.633 - 1.644 nγ = 1.638 - 1.650
Birefringence	δ = 0.009 - 0.010
Pleochroism	Weak
2V angle	71 - 86°
Dispersion	r < v strong
Ultraviolet fluorescence	non-fluorescent
References

Andalusite is an aluminium nesosilicate mineral wi the chemical formula Al₂SiO₅.