Precious and Decorative Stones

2024: No. 2 (116) CONTENTS

DOI: https://doi.org/10.53036/2024-2(116)-2

GEMOLOGICAL RESEARCH OF THE UNTREATED YELLOW SAPPHIRE

Yu. Gayevsky
State Gemmological Centre of Ukraine

Yu. Ladzhun
State Gemmological Centre of Ukraine

Language: Ukrainian

Precious and Decorative Stones. No.2 (116), 2024: 12–14

Abstract
The purpose of this gemological study is to establish the name, origin and heat-treatment of the yellow faceted stone. The characteristic features of this cut stone were established: optical character of the stone (1-), refractive index (No = 1.769, Ne = 1.761), birefringence (0.008), specific gravity (3.99 g/cm3), pleochroism (weak), fluorescence in the long-wave range (365 nm) is yellow, fluorescence in the short-wave range (254 nm) is orange-yellow. Studies by the method of semi-quantitative X-ray fluorescence analysis (EXDRF) showed a very small amount of Fe, Cr, Ti, V oxide impurities. The study using the IR-Fourier spectroscopy method revealed absorption peaks around 3166, 3155, 3240, см-1. Microscopic examination of the stone's internal inclusions established the presence of a large cloud of linearly oriented points and microneedles. Along with it, long needle-like inclusions were found. The totality of the obtained data shows that the stone submitted for examination comes from a metamorphic deposit and does not heat treatment. This confirms the information of the client of the examination that this stone was extracted from placer deposits in the central part of the island of Sri Lanka at the famous Ratnapura gem deposit. According to literature, these placers were formed as a result of long-term destruction of various Precambrian metamorphic rocks (charnockites, granulites, gneisses) and younger ones (granites, pegmatites). Unheated yellow sapphires are rare, since the vast majority of such stones are heat treated in color on the Ukrainian jewelry market.

Keywords: yellow sapphire, complex gemological research, microscopy, X-ray fluorescence analysis, IR-Fourier spectroscopy.

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