On the dispersion of idocrase
Abstract
In the third issue of Fedorov's "Universal Method," in Chapter VII — "Study of Dispersion" — V. V. Nikitin describes idocrase exhibiting sharp dispersion of birefringence. Furthermore, it possesses the property that within a single grain, in its various sections, the magnitude of birefringence varies. As a result, the interference color is not uniform across the entire extent of the idocrase grains. In sections close to parallel to the optical axis — the fourfold axis of symmetry of the crystal — the colors are arranged in bands parallel to each other: the central part of the grain shows white interference color, followed by a band with a mastix-yellow color, then a purple-red one, and finally, the edges of the grain are colored purple-violet.
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