|Emerald macro-crystal from Brazil, 2 mm
thick. The slight pleochroism between two different hues of green is due
to the slight change in the position of the bands which widen or narrow
the band pass in the green part of the spectrum. The 2 bands structure
at 430 and 600 nm can be assigned to allowed crystal field transitions
of the Cr3+ impurities. The narrow peaks superimposed on the
wide bands are forbidden transitions.