Andesine

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Andesine
Chemical composition (Na,Ca)[Al(Si,Al)Si2O8]
Crystal system Triclinic
Habit Prismatic
Cleavage Distinct to perfect
Fracture Conchoidal
Hardness 6.5
Optic nature Biaxial +/-
Refractive index 1.551 - 1.560
Birefringence 0.009
Specific gravity 2.67
Lustre Sub-vitreous
Congolese andesine