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CRYSTAL AND CHEMICAL CHARACTERISTICS AND NATURE OF COLORATION OF CHRYSOBERYL AND ALEXANDRITE JEWELRY FROM THE URAL EMERALD MINES

M. P. Popov

Abstract

In paper describes the geological structure and mineral associations of the Ural emerald mines (Middle Urals, Russia) as the main source of high-quality chrysoberyl and its rare variety, alexandrite. The purpose of work is to identify the crystal chemical characteristics and nature of the color of natural chrysoberyl and alexandrite, as well as to study the comparative crystal chemical characteristics with their synthetic analogs. Samples for research were chrysoberyl and alexandrite from mica carrying rocks and pegmatite of the Ural emerald mines, as well as their synthetic analogs grew by the solution-melt method. The studies have done by the method of optical absorption spectroscopy. Optical absorption spectra were recorded on an MSFP - K standardized spectrophotometer. The registration of optical absorption spectra was performed in the wavelength range of 400 - 800 nm, with a step of 1 nm. The results of analyzes showed the main chromophore for the color of chrysoberyl is trivalent iron, for the color of alexandrite is trivalent chromium. In work, the nature of the color was revealed of natural alexandrites and their synthetic analogs, using the methods of optical spectroscopy, the main colorimetric parameters of the color reverse were calculated for them. With an increase in the relative content of Cr3+ ions, the saturation of the basic color tone of alexandrites increases and the parameters of the reverse is enhanced. Alexandrite, taken from pegmatite veins, contains the most minimal intensity bands of chromium absorption, and therefore they can be attributed to chrysoberyl. Samples containing the maximum intensity bands of chromium are arranged in mica carrying rocks.

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