Grandidierite: gemological and mineralogical studies
| N. Vovk Brand owner N.VOVK jewelry ORCID: 0009-0007-3454-9447 |
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Yu. Gayevsky Gemological Centre of Ukraine ORCID: 0009-0005-4781-0806 |
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Ye. Naumenko National Natural Science Museum of the NAS of Ukraine ORCID: 0000-0001-5323-4706 |
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Yu. Yavdoshchuk National Taras Shevchenko University of Kyiv |
| Language: Ukrainian |
| Precious and Decorative Stones. No. 1 (123), 2026: 4–11 |
| Abstract In the article, the authors investigate faceted grandidierites of jewelry quality and untreated grandidierite crystals. The relationship between the structure of grandidierite and its optical properties, primarily with biaxiality, is shown, the symmetry of grandidierite is demonstrated using the example of untreated crystals, and conclusions are drawn regarding the optical orientation of the faceted stone to obtain maximum color saturation. According to chemical analysis, the dependence of the degree of color saturation on the number of Fe2+ impurity atoms that replace Al3+ in the trigonal-dipyramidal polyhedra of the crystal structure of grandidierite is proven. The gemological characteristics of faceted grandidierites are determined: refractive index, birefringence, optical sign, presence of luminescence and specific gravity, as well as the color palette of grandidierite according to GIA Gemset standards. According to gemological characteristics, faceted grandidierites were compared with similar-colored minerals that can also be used as faceted gemstones – with lazulite, apatite, tourmaline and fluorite, and a diagnostic algorithm was built. Microscopic study allowed us to record the presence of gas-liquid and multiphase inclusions, as well as to detect the refinement of several samples by filling cavities with organic matter. Research by IR-Fourier spectroscopy allowed us to obtain data on the correspondence of certain absorption peaks and vibrations of certain groups in the crystal lattice of grandidierite, as well as to confirm the refinement of faceted grandidierites by filling cracks with organic matter, and even to determine the nature of the corresponding substance. These data can also be used not only in the diagnosis of grandidierite as such, but also to determine the presence of its refinement, which was previously unknown in the world. Such a comprehensive study of grandidierite as a rare gemstone is a first not only for the Ukrainian market, but also opens new pages in global gemological practice. |
| Keywords: grandidierite, gemological studies, refractive index, refinement, surface filling, mineral inclusions. |
| References |
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