Light waves transmitted parallel to the c-crystallographic axis vibrate parallel to the planes of the carbonate ions, increasing polarization already present. Calcite therefore shows a relatively high index of refraction and a corresponding low velocity for waves advancing parallel to c, regardless of their vibrational direction normal to the axis. Light waves transmitted through the calcite crystal perpendicular to the c- crystallographic axis advance with different velocities depending upon their vibrational direction. Waves vibrating perpendicular to c also vibrate in the plane of the carbonate ions, increasing polarization and advancing with the same velocity as waves transmitted parallel to c. Nicol prism -a polarizing prism made of calcite cut at a specific angle.
Nicol prisms are extremely precise, but very expensive.
In effect, it plane polarizes the incident light beam. Analyzer -a polarizing prism located above the microscope stage, between th esection and the eyepiece. This restricts the transmission of light vibrating perpendicular to the polarizer. The analyzer can be slipped in oro out of the light path. Light passing through the polarizer will not pass through the analyzer unless the vibration direction of the light is changed between the two prisms.