Some crystals show distinctive zones due to variations in their composition during the growth phase.
These zones are frequently concentric (the one on the right with the first-order quartz compensating sheet):
But they can also show other arrangements that reflect the internal symmetry of the crystal.
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Although to observe the zonation you usually need to work with the built-in polarizer and analyzer (XPL) on rare occasions it is possible to observe the zonation directly without polarized light as is the case with these tourmaline crystals.
Index | Introduction | PPL | XPL ortos