Tourmaline vs biotite pleochroism

Tourmaline and biotite have similar colors of pleochroism, but biotite shows darker colors when its long axes are parallel to the horizontal (the polarizer), whereas tourmaline when it is oriented vertically or perpendicular to the horizontal, as shown in the video.

Biotite: maximum colors when oriented E-W.
Tourmaline: maximum colors when oriented N-S.

PPL. Width: 3 mm.
Calamita, Island of Elba, Italy.

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