Relationship between the colour of ochre from Roussillon and the content of iron-bearing minerals

Nine samples of ochre from Sentier des Ocres near Roussillon, France, were studied with Mössbauer spectroscopy and spectro-photo-colourimetry. Mössbauer spectroscopy was used for quantitative phase analysis of iron-containing minerals (goethite, hematite and kaolinite). Colourimetry enabled determination of the CIE-L*a*b* colour coefficients. Both a⁎ and b⁎ coordinates are responsible for the colour of the ochres. The colour coordinate a⁎ was positively correlated with the content of hematite, negatively with that of goethite and kaolinite. The coordinate b⁎ was positively correlated with the relative amount of goethite, negatively correlated with that of hematite, and weakly correlated with the amount of kaolinite. With respect to L⁎, a⁎ showed negative correlation, and b⁎ showed positive correlation.