Examination of the microstructure and composition of jadeite jade - a combination of X-ray microtomography and petrographic methods

High-quality jadeite jade is one of the most valuable gemstone materials in the jewellery trade. In addition to colour and translucency, mineralogical homogeneity and the absence of cracks are crucial for the quality of jadeite jade. The last two characteristics were investigated using a combination of petrographic methods and X-ray microtomography. High-quality jade monomineralically consists of jadeite and has a fine, polycrystalline structure. However, such high-quality jade was deliberately avoided for the examinations presented here, as the main aim of this study was the identification of different mineralogical phases by X-ray microtomography and their determination by petrographic methods. The overall goal was to create a database in which each mineralogical phase is assigned a characteristic value corresponding to its attenuation coefficient, in order to use non-destructive X-ray microtomography as a tool for the precise examination of mineralogically inhomogeneous jadeite samples. The attenuation coefficient is a material dependent constant with the unit cm -1, which expresses the ability of a mineral phase to attenuate X-rays. With a computer tomography (CT) scan, the values are presented in shades of grey as a tomogram. If the settings remain the same, these values are comparable for measurements on the same device. Comparing the attenuation coefficients of mineral phases to identify their composition is a well-known technique. For this purpose, a program can be used to visualize the minerals present based on their attenuation values (Bam et al. 2020). However, in addition to the density of the material and the energy of the X-rays, the chemical formula of the minerals must be known, which is not the case for unworked jade specimens. In general, the attenuation coefficient decreases with increasing energy of the X-rays, decreasing density of the material and lower atomic numbers of the elements present in the material (Bam et al. 2020).