Gemmological and Spectral Characteristics of Triplite from Pakistan

Triplite is a primary mineral in phosphorus-rich granite. It is one of the rarest gems that has been discovered recently in Pakistan. 5 pieces of triplite samples from Pakistan were collected and studied by conventional gemmological tests and advanced instrumentation including energy dispersive X-ray fluorescence spectrometer, EPMA, UV-Vis, Fourier transform infrared spectrometer, and Raman spectrometer. The results showed the colour of the triplite is from orange yellow to orange, and its polished facet shows glassy lustre. It showedinert under LW and SW ultra-violet lamp.The refractive index is 1.662-1.690, and birefringence is 0.026. The density is 3.6-3.8 g/cm³, and its Mohs hardness is 5-6. Triplite has characteristic Raman and FTIR spectra. FTIR results indicate that the most characteristic part is O-P-O stretch vibration between 900-1 200 cm^-1, absorption peaks around 400-700 cm^-1 belong to bending vibration and stretch vibration.And its Raman spectrum shows peaks of 428、455、610、980、1 037、1 071、1 129 cm^-1 and 3 451-3 471 cm^-1 are triplite's identification bases. EPMA and XRF result show Fe, Mn, P and other elements from tested samples which meets triplite's chemical formula (Mn, Fe)₂(PO₄)F. Through the analysis of UV-Vis fluorescence spectra, it can be concluded that the colour of triplite may be related to its Mn²⁺ and Fe²⁺ ions element. The colour of the sample deepens with the increase of Fe²⁺ ions content.