Lecontite, (NH4)Na(SO4).2H(2)O, was synthesised at room temperature in high purity compared to earlier work with a minor impurity of mascagnite, (NH4)(2)SO4. Rietveld refinement of the XRD results confirmed the crystal structure and unit cell dimensions as published earlier. Raman and Infrared spectroscopy, in conjunction with factor group analysis, resulted in a complex pattern of overlapping sulphate, NH and OH modes. The NH modes upsilon(1) was observed around 2880 cm(-1), upsilon(2) around 1700 cm(-1) overlapping with water OH-bending modes, upsilon(3) around 3300 cm(-1) overlapping with water OH-stretching modes around 3023, 3185 and 3422 cm(-1), and upsilon(4) around 1432, 1447 and 1462 cm(-1). The sulphate group in the crystal structure displays a decrease in symmetry from T-d as evidenced by the activation of the nu(1) mode at 982 cm(-1) and the nu(2) mode around 452 cm(-1) in the Infrared spectrum. The upsilon(3) mode shows clear splitting in the infrared spectra with a strong band at 1064 cm(-1) accompanied by two shoulders at 1107 and 1139 cm(-1). The Raman spectra show three weak bands at 1068, 1109 and 1135 cm(-1) with a shoulder at 1155 cm(-1). Similar splitting was observed for the upsilon(4) mode around 611 and 632 cm(-1) in the Infrared and Raman spectra, respectively.