Characterization and comparison of natural and Zachery-treated turquoise: new data

IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY
Valeria Diella, Marco Cantaluppi, Rosangela Bocchio, Elena Possenti, Ilaria Adamo, Giancarlo Della Ventura, Lucia Mancini, Nicoletta Marinoni
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Abstract

Turquoise is a well-known gemstone that has been used in artefacts across many cultures throughout history. However, due to its porosity it is often treated to enhance its color and beauty. One appreciated treatment is the patented Zachery process, although its details remain publicly undisclosed. Previous studies indicated that only a high K content distinguishes Zachery-treated from natural turquoises. In this study, natural and Zachery-treated turquoise samples from the famous Kingman mine, Arizona, USA, were analysed by means a multi-methodological approach, including standard gemological testing, electron microprobe (EMPA), scanning electron microscope with energy dispersive spectrometer (SEM–EDS) and X-ray diffraction (XRD), Fourier-Transform InfraRed (FTIR), non-destructive External Reflection-Fourier-Transform InfraRed (ER-FTIR) spectroscopy and X-ray computed microtomography (μCT). The results revealed new chemical–mineralogical and microstructural features that distinguish the Zackery-treated from the natural turquoise: higher specific gravity and lower porosity, associated with high and uneven concentrations of Cu, K and Na, the occurrence of tenorite (CuO), the presence and extension of reaction edges in the entire volume are distinctive of treated samples. Moreover, Cu-rich seeds and feldspar crystals may be interpreted as additional components used during the treatment. The hypothesis is that the Zachery treatment induces the re-crystallization of a new turquoise-like phase, which differs from the natural one from a chemical and microstructural point of view.

Abstract Image

天然绿松石和zachery处理绿松石的特性和比较:新数据
绿松石是一种众所周知的宝石,在历史上许多文化中都被用于人工制品。然而,由于其多孔性,它经常被处理以增强其颜色和美观。一种受欢迎的治疗方法是获得专利的Zachery方法,尽管其细节尚未公开。先前的研究表明,只有高钾含量才能将扎克里处理的绿松石与天然绿松石区分开来。采用标准宝石学检测、电子探针(EMPA)、扫描电子能谱仪(SEM-EDS)和x射线衍射仪(XRD)、傅里叶变换红外(FTIR)、无损外反射-傅里叶变换红外(ER-FTIR)光谱和x射线计算机显微断层扫描(μCT)等多种方法对美国亚利桑那州著名的金曼矿的天然绿松石和经zachry处理的绿松石样品进行了分析。研究结果揭示了与天然绿松石不同的化学矿物学和微观结构特征:较高的比重和较低的孔隙度,Cu、K和Na浓度高且不均匀,铜钼矿(CuO)的存在,反应边缘的存在和延伸是处理样品的特征。此外,富铜种子和长石晶体可能被解释为处理过程中使用的附加成分。假设是,Zachery处理诱导了一种新的绿松石样相的再结晶,从化学和微观结构的角度来看,这种相与自然相不同。
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来源期刊
Physics and Chemistry of Minerals
Physics and Chemistry of Minerals 地学-材料科学:综合
CiteScore
2.90
自引率
14.30%
发文量
43
审稿时长
3 months
期刊介绍: Physics and Chemistry of Minerals is an international journal devoted to publishing articles and short communications of physical or chemical studies on minerals or solids related to minerals. The aim of the journal is to support competent interdisciplinary work in mineralogy and physics or chemistry. Particular emphasis is placed on applications of modern techniques or new theories and models to interpret atomic structures and physical or chemical properties of minerals. Some subjects of interest are: -Relationships between atomic structure and crystalline state (structures of various states, crystal energies, crystal growth, thermodynamic studies, phase transformations, solid solution, exsolution phenomena, etc.) -General solid state spectroscopy (ultraviolet, visible, infrared, Raman, ESCA, luminescence, X-ray, electron paramagnetic resonance, nuclear magnetic resonance, gamma ray resonance, etc.) -Experimental and theoretical analysis of chemical bonding in minerals (application of crystal field, molecular orbital, band theories, etc.) -Physical properties (magnetic, mechanical, electric, optical, thermodynamic, etc.) -Relations between thermal expansion, compressibility, elastic constants, and fundamental properties of atomic structure, particularly as applied to geophysical problems -Electron microscopy in support of physical and chemical studies -Computational methods in the study of the structure and properties of minerals -Mineral surfaces (experimental methods, structure and properties)
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