Template:Feldspar

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Feldspar
Chemical composition Potassium, Sodium and Calcium-Aluminium Silicates

I. K-Feldspar (KALSi308)
II . Plagioclase Feldspar (isomorphous)

Crystal system monoclinic - triclinic
Habit prismatic, often twinned
Cleavage good to perfect
Fracture conchoidal
Hardness 6
Optic nature biaxial -
Refractive index 1.52 - 1.53 (K-Feldspar)

1.52 - 1.57 (Plagioclase)

Birefringence 0.006 - 0.007 (K-Feldspar)

0.008 - 0.011 (Plagioclase)

Specific gravity 2.55 - 2,58 (K-Feldspar)

2.60 - 2.80 (Plagioclase)

Lustre vitreous