A related phenomenon is the formation of pleochroic halos surrounding minute zircon inclusions within a crystal of biotite or other mineral.
2.
Pleochroism is often especially intense in small spots which surround minute enclosures of other minerals, such as zircon and epidote, these are known as " pleochroic halos ."
3.
In the latter case, the decay of a radioactive element damages the mineral crystal; the result, termed a " radioactive halo " or " pleochroic halo ", is observable by various techniques, such as thin-section petrography.
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