This page summarize the pleochroism of glaucophane family.
The 3 small crystals sections are about 90° from each other: left crystal
is purple-blue (g-b), the center one is
no color-violet (a-g) and the crystal to
the right is no color-blue (a-b).
Spectra of the small crystal to the left of the pictures
above (size about 400 µ).