Double refraction in calcite3D Model
This model depicts the double refraction properties of calcite (and other birefringent minerals). It shows the splitting of incident light into two rays (E-ray and O-ray) which are both polarised and have vibration planes perpendicular to each other. Importantly, these rays travel at different speeds through the crystal, and in the case of calcite, the E-ray travels faster than the O-ray (referred to as optically negative). Under cross-polarised light this difference in speed produces an interference phenomenon called birefringence. In the case of calcite, the difference in refraction is so marked that two images can be seen through transparent hand specimens.
“E-ray” is short for extraordinary ray and its vibration direction (referred to as epsilon) is parallel to the optic axis (O.A.). “O-ray” is short for ordinary ray and its vibration direction (referred to as omega) is perpendicular to the optic axis.
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