Vibrational spectroscopy of synthetic archerite (K,NH4)H2PO4- and in comparison with the natural cave mineral

In order to mimic the formation of archerite in cave minerals, the mineral analogue has been synthesised. The cave mineral is formed by the reaction of the chemicals in bat guano with calcite substrates. X-ray diffraction proves that the synthesised archerite analogue was pure and more pure than the natural cave mineral. The vibrational spectra of the synthesised mineral are compared with that of the natural cave mineral from the Murra-el-elevyn Cave, Eucla, Western Australia. Raman and infrared bands are assigned to H2PO4-, OH and NH stretching and bending vibrations. The Raman band at 917 cm−1 is assigned to the HOP stretching vibration of H2PO4- units. Bands in the 1200–1800 cm−1 region are associated with NH4+ bending modes. Vibrational spectroscopy enables the molecular structure of archerite analogue to be analysed.

► We have synthesised the analogue of the cave mineral archerite ((K,NH4)H2PO4).
► The molecular structure of the archerite analogue has been determined and compared with that of the natural cave mineral.
► Raman spectroscopy has been used to characterise these ‘cave’ minerals.
► The mineral is formed by the reaction of the chemicals in bat guano on calcite substrates.