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Colloidal gold as a colouring principle in minerals

Published online by Cambridge University Press:  14 March 2018

J. Newton Friend
Affiliation:
Central Technical College, Birmingham
John P. Allchin
Affiliation:
Central Technical College, Birmingham

Extract

Many attempts have been made to discover the causes of the various colours displayed by minerals. If we except fluorescence and allied phenomena, the diiteren~ theories advanced may in general be grouped under one or other of the following classes:

  1. (1) Colour may be due to an intrinsic property of atoms, ions, or molecules. Examples are copper atoms, chromate ions, and ferric oxide molecules.

  2. (2) Colour is sometimes attributed to structural causes. The blue tints of certain halites have been explained in this way; but a fresh suggestion is made in this communication.

  3. (3) A pigmentary impurity may cause the observed colour. The colour of the ruby is believed to be caused by the presence of a red chromic oxide. The blue tint of a Yorkshire aragonite is shown later to be due to a copper salt.

  4. (4) Some minerals show plays of colours due to interference and/or grating effects. Labradorite and opal are cases in point. Into this group also fall minerals like bomite which become iridescent from tarnish.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1940

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