Template:Sillimanite

From The Gemology Project
Jump to: navigation, search
Sillimanite
Chemical composition Al2SiO5
Crystal system Orthorhombic
Habit Long slender prisms, fibrous
Cleavage Good, prismatic {010}
Fracture Uneven, brittle
Hardness 6 - 7.5
Optic nature Biaxial +
Refractive index 1.653 - 1.685
Birefringence 0.014 - 0.021
Dispersion Low, 0.015
Specific gravity 3.20 - 3.26
Lustre Vitreous to silky
Pleochroism Strongly trichroic