Gemmological and Mineralogical Characteristics of Light Blue-Green Phosphophyllite from Bolivia

Phosphophyllite is a rare gemstone. Currently, there is little gemmological and spectroscopic characteristic study on phosphophyllite in China. Detailed determination and analysis of a light blue-green phosphophyllite sample from Bolivia was carried out by X-ray fluorescence spectroscopy (XRF), electron probe (EPMA), laser Raman spectrometer (Raman), infrared spectrometer, UV-Vis spectrophotometer and other test apparatuses. XRF analysis showed that Fe, Zn, P were the main elements of phosphophyllite, and there were Mn, Na, K, Ca and other trace elements in phosphophyllite. The quantitative analysis of Fe, Zn, P and Mn elements in Bolivian phosphophyllite was carried out by electron probe. The average molecular formula was Zn_2.18(Fe_0.92Mn_0.01)(P_0.99O₄)₂·4H₂O. Raman spectrum test shows that the Raman peak at 325 cm^-1 is caused by M-O (M is metal cation Zn²⁺, Fe²⁺, Mn²⁺) vibration, and the Raman peak at 400-1 200 cm^-1 is caused by PO₄^3-, the Raman peaks at 1 602, 3 153, 3 374 cm^-1 and 3 566 cm^-1 are caused by the vibration of water molecules. The dark brown associated mineral on the phosphophyllite sample from Bolivia is sphalerite, and the Raman shifts are at 228, 304, 351 cm^-1.Infrared spectrum test shows that the band in the range of 400-1 200 cm^-1 is caused by PO₄^3-, and the band in the range of 1 600-3 600 cm^-1 is caused by the vibration of water molecules, and the white associated mineral on phosphophyllite sapmle from Bolivia is illite, whose absorption peaks are at 3 650, 3 625, 3 425, 1 646, 1 028, 538, 474, 418 cm^-1.The UV-Vis spectrophotometer test shows that the absorption line of phosphophyllite is consistent with the ferrographic characteristic of three strong absorption bands at blue-green region of 380, 448 nm and 467 nm, indicating that the main chromogenic element of phosphophyllite is Fe²⁺.The absorption band at 501 nm was consistent with the manganese spectroscopy characteristic, indicating that the chromogenic element of phosphophyllite may also be Mn³⁺.