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ABSORPTION EFFECTS: COLOUR, DICHROISM, ETC.

WHEN white light passes through a cut stone, colour effects result which arise from a variety of causes. The most obvious is the fundamental colour of the stone, which is due to its selective absorption of the light passing through it, and would characterize it before it was cut. Intermingled with the colour in a transparent stone is the dispersive effect known as ‘fire,’ which has already been discussed (p. 20). In many instances the want of homogeneity is responsible for some peculiar effects such as opalescence, chatoyancy, and asterism. These phenomena will now be considered in fuller detail.