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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. [ABSTRACT FROM AUTHOR]

This paper presents geology aspects of jeweler demantoid new manifestation, which was recently discovered in the Polar Urals. The mineralogical characteristics of the manifestation are described, demantoids chemical analysis results are shown, and comparative analysis of demantoids with samples from classical Ural deposits is given. The crystal chemical characteristics of demantoids from this manifestation are studied and color origin of these garnets is investigated. Demantoid mineralization is presented in two types: single rounded grains and granular discharges from 2 to 5 mm, which form small chains up to 1-2 cm; edges of the garnet. The garnet purity is low; there are numerous inclusions of tremolite, gas-liquid inclusions, hollow channels and cracks. Crystals are categorized as cleanliness 2. The presence of byssolite is the most characteristic sign for demantoids under study (the “horse tail” inclusion). The nature of byssolite distribution, morphology of its aggregates allows us to talk about several types: clustered secretions; needle inclusions; matted-fibrous aggregates. The Skalny manifestation is confined to the western endocontact of the ultra-massif Cyum-Keu massif and is represented by veins zone, in which there are numerous veins of jadeite, albite-jadeite and plagioclase-jadeite bodies. The host rocks for garnets are serpentized ultrabasic rocks. Aggregates are found in cracks (rupture) which filled by tremolite. Demantoids comparative analysis of the Skalny manifestation and famous Ural field the Novo-Karkodinskoe deposits (Middle Urals) with following comparison criteria were used: geology, deposit, structure of veins, morphology, gemological characteristics. Garnet mineralization was studied in the Skalny manifestation and garnet group mineralogical series was established: andradite, demantoid, topazolite and uvarovite. Together with garnet, talc, antigorite, tremolite and chromite are found. The noble varieties of andradite (topazolite, demantoid) can be used as a material for obtaining gemstones of average quality. [ABSTRACT FROM AUTHOR]