Precious and Decorative Stones

2025: No. 1–2 (119–120) CONTENTS

DOI: https://doi.org/10.53036/2024-2(116)-1

Identification of natural turquoise imitation with Cu-bearing faustite using raman spectroscopy

О. Portyanko
LLC "N CONSULTING"

V. Surova
State Gemmological Centre of Ukraine

Language: Ukrainian

Precious and Decorative Stones. No. 1–2 (119–120), 2025: 4–8

Abstract
This paper presents the results of a comprehensive gemological, optical-microscopic, and chemical study of a blue-colored insert from a piece of jewelry submitted for examination to accurately identify the mineral. Blue minerals have long held high aesthetic and cultural value; however, only modern analytical methods allow for the identification of minerals that are similar in appearance but differ in composition. Particular attention is given to turquoise and related minerals, which are often confused with one another due to similarities in color and luster. The research was carried out using standard gemological equipment (refractometer, UV lamp, Mohs hardness scale), microscopy with various illuminators and filters, energy-dispersive X-ray fluorescence spectrometry (EDXRF), and Raman spectroscopy. It was determined that the insert has a greenish-blue color, a semi-transparent structure, inclusions of pyrite and quartz, and a refractive index in the range of n = 1.60–1.61. Chemical analysis revealed a predominance of zinc oxide (ZnO) over copper oxide (CuO), which does not correspond to the typical composition of classical turquoise. Based on spectral characteristics and physico-optical properties, the sample was identified as copper-bearing faustite – the zinc analog of turquoise. Considering the impurity content, optical behavior, and comparative spectral data, the mineral is classified as belonging to the turquoise group, though not turquoise itself, but rather its zinc-substituted variation. This study highlights the importance of using modern spectral analysis techniques in gemology, enabling the elimination of erroneous classifications of natural minerals and ensuring accurate scientific attribution.

Keywords: turquoise, faustite, Cu-containing faustite, natural imitation of turquoise.

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