The distinction between these minerals cannot easily be made in the field. The composition can be roughly determined by specific gravity, but accurate measurement requires chemical or optical tests. The composition in a crushed grain mount can be obtained by the Tsuboi method, which yields an accurate measurement of the minimum refractive index that in turn gives an accurate composition. In thin section, the composition can be determined by either the Michel Lévy or Carlsbad-albite methods. The former relies on accurate measure of minimum index of refraction, while the latter relies on measuring the extinction angle under a polarizing microscope. The extinction angle is an optical characteristic and varies with the albite fraction (%Ab).
The distinction between these minerals cannot easily be made in the field The composition can be roughly determined by specific gravity but accurate measurement requires chemical or optical tests The composition in a crushed grain mount can be obtained by the Tsuboi method which yields an accurate measurement of the minimum refractive index that in turn gives an accurate composition In thin section the composition can be determined by either the Michel Lévy or Carlsbad-albite methods The former relies on accurate measure of minimum index of refraction while the latter relies on measuring the extinction angle under a polarizing microscope The extinction angle is an optical characteristic and varies with the albite fraction (%Ab)