Relation between the interference colour and the interference figure


The interference colour of a group of mineral grains is related to their interference figure.

For instance, in a uniaxial crystal (quartz in the picture), as the cut becomes more inclined from the horizontal to vertical, the interference colour becomes higher, whilst in the interference figure, the centre of the cross moves away from the centre of the field of view until it disappears (in the case of very inclined cuts). The vertical cut shows the maximum interference colour and a flash interference figure, whilst the horizontal cut shows a minimum interference colour (black) and in its interference figure the centre of the cross coincides with the centre of the field of view.

Biaxial crystal case.


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