The quantitative measurement of colour in minerals

Abstract

The present study has been directed towards investigating quantitative measurements of colours in minerals, which might serve as a readily accessible means of identification and understanding related properties. A review of the concepts of colour measurement is described in the first part of the thesis. Attention has been paid to the improvement and application of methods of colour measurement,- in mineralogy and gemmology. Computational procedures and all the necessary computer programmes for calculating colour values are given with examples. For this purpose appropriate measurements of spectral reflectivity for opaque minerals, and spectral transmittance for non-opaque minerals and facetted gemstones are described. Quantitative measurements of other colour properties - colour constancy, bireflectance and reflection pleochroism - are described and defined. A study of some colour problems in ore minerals is made. Tables of colour values and spectral reflectivity data for 130 ore minerals are given, and these values are also presented in colour diagrams. The uses of quantitative colour values and colour diagrams are explained with examples.