Original paper
A revised Michel-Lévy interference colour chart based on first-principles calculations
Sørensen, Bjørn Eske
European Journal of Mineralogy Volume 25 Number 1 (2013), p. 5 - 10
published: Feb 11, 2013
DOI: 10.1127/0935-1221/2013/0025-2252
Open Access (paper may be downloaded free of charge)
Abstract
Two revisions of the original Michel-Lévy interference colour chart are presented, and discussed here. Compared to older charts these give a more precise match to the actual observations in the modern optical microscope. As an example, interference colour transitions on wedge shaped olivine grain boundaries toward epoxy match accurately the interference colour in the new charts. The differences in the colour between older charts and the new are most pronounced in the second order, where the saturated green is now replaced by greenish white and turquoise. In addition, the pinks are shown to cover a larger range than previously thought. The revised charts make it easier to determine interference colour and order, and hence also to determine the birefringence of the common silicate minerals. Because of the first-principle origin of the charts it is easy to adjust the charts for different types of optics and illumination. Also the improved understanding of interference colour opens up new possibilities in image analysis of transmitted-light images involving interference colour.
Keywords
optical microscopy • interference colour chart • michel-lÉvy • interference colour • optical mineralogy • birefringence • optical crystallography