Aluminium Silicate
Al2SiO5
Chemical name
Aluminium Silicate
Mineral name
Andalusite
Chemical formula
Al2SiO5
Crystal system
orthorhombic
Crystal Class
orthorhombic-dipyramidal (2/m 2/m 2/m)
Space Group
Pnnm
Unit cell
a [Å]:7.78
b [Å]:7.92
c [Å]:5.57
Molecular weight [g/mol]
162,03
Formula units
Z=4
Frequent crystal surfaces
{110}, {001}
Twinning
rare on {101}
Mohs hardness
6.5 - 7.5
Density [g/cm3]
3.13 - 3.16
Cleavage
perfect on {110}
Fracture / Tenacity
brittle to subconchoidal
Color
pink, violet, yellow, green, white, gray
Streak
white
Transparency
transparent to nearly opaque
Optical character
biaxial (-)
Refractive Index
nα=1.629-1.640; nβ=1.633-1.644; nΥ=1.638-1.650
Birefringence δ
0.009 - 0.010
Pleochroism δ
strongly trichroic