A plagioclase feldspar with 70-90% anorthite and 10-30% albite. Bytownite is at the "high" end of the series and has an RI slightly higher than that normally given for feldspar as a whole.

Physical properties:

Chemistry: Na[AlSi3O8] Ca[Al2Si2O6]
Hardness: 6-6.5
SG: 2.74-2.75
Cleavage: Perfect, three directions
Fracture: Somewhat brittle
Thermal sensitivity: None

Optical properties:

RI: 1.56-1.58
Dispersion: 0.012 (weak)
Double refraction: 0.008 (weak)
Pleochroism: None
Critical angle: 40°

Facet angles (pavilion/crown):

Vargas: 44°/42°
Olson: 43°/42°
Soukup: 43°/42°
Roth: 43°/42°
MDR: 43°/42°
Schlagel: 43°/39°
Hashnu: 43°/42°
Sinkankas: 43°/40-50°
GIA: 43°/42°
Perkins: 43°/39°
Raytech: 43°/42°

Cutting lap:

Medium or fine

Faceting polishing:

Vargas: Cerium oxide on acrylic, Aluminum oxide on tin/lead
Olson: Tin oxide on acrylic
Christiansen: Aluminum oxide on tin/lead, Cerium oxide on acrylic, Tin oxide on tin
Perkins: Aluminum oxide on BATT or Corian
Raytech: Cerium oxide on Fast Lap, phenolic or acrylic

Cabochon polishing:

Olson: Tin oxide on felt
Christiansen: Aluminum/cerium oxide on leather or felt
Cox: Cerium oxide on felt
Covington: Cerium oxide on felt


After shape. Usually, even the table facet does not need to be oriented away from the cleavage plane.


None known (some sources claim that Chinese andesine is heat-treated bytownite from Mexico)


Sometimes it can be difficult to polish - try using a LightningLap CeOx for better results.

Bytownite rough

Bytownite on Gemdat

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