Gemmological Characteristic of A Kind of Purple Jade: Phosphosiderite

To analyze the difference between a kind of purple jade called "American mica jade" recently appeared in Anhui market and its similar gemstones, as well as the component of the white and purple minerals in the purple jade, the gem microscope, refractometer, UV-Vis, FTIR, EPMA and XRD were used in this paper. The results showed that the infrared spectra of the purple jade samples have 3 382、3 114、1 634 cm^-1peaks caused by crystal water, and peaks near 1 025、594、469 cm^-1 caused by PO₄^3- which are not characteristic absorptions of mica. The peak at 1 511 cm^-1 is caused by the bending vibration of bisphenol A epoxy resin. X-ray diffraction data showed that the main constituent mineral of the purple jade sample is pure phosphosiderite (also known as chinostrengite). Electron probe assay showed that the chemical formula of purple jade samples is FeSO₄·2H₂O. The strong absorption peak near 434 nm, and wide absorption peak near 539 nm and 751 nm can be seen in the UV spectra. It was proved that the the purple jade sample has been filled but not dyed. The Raman spectra of the purple and white minerals in the purple jade sample were basically consistent. The SEM result showed that the main elements of the purple and white minerals are the same, only the densities are different. Therefore, the colour difference may be attributed to different density.