Raman study of natural berlinite from a geological phosphate deposit

Natural berlinite from a heated sedimentary sequence in Cioclovina Cave (Romania) was studied using Raman spectroscopy complemented with infrared techniques. Vibrational data acquired at room temperature were compared with those reported for synthetic berlinite in ambient conditions. The symmetry of the (PO4)3− units is confirmed by the observation of characteristic bands attributed to the ν1(PO4)3− stretching mode, both the ν4 and ν2 bending regions at 500–595 cm−1, and 350–500 cm−1, respectively. The berlinite Raman fingerprint was unambiguously identified at 1111 and 1104 cm−1, confirming the identity of the species and elucidating some controversial reports in the mineralogy field.The vibrational data of natural berlinite relates to its crystallography, and along with the spectra–structure correlation, confirmed an almost ideal natural berlinite crystal.