The molecular structure of the sodium borate mineral ameghinite NaB(3)O(3)(OH)(4) has been determined by the use of vibrational spectroscopy. The crystal structure consists of isolated [B(3)O(3)(OH)(4)](-) units formed by one tetrahedron and two triangles. H bonds and Na atoms link these polyanions to form a three-dimensional framework. The Raman spectrum is dominated by an intense band at 1027 cm(-1), attributed to BO stretching vibrations of both the trigonal and tetrahedral boron. A series of Raman bands at 1213, 1245 and 1281 cm(-1) are ascribed to BOH in-plane bending modes. The infrared spectra are characterized by strong overlap of broad multiple bands. An intense Raman band found at 620 cm(-1) is attributed to the bending modes of trigonal and tetrahedral boron. Multiple Raman bands in the OH stretching region are observed at 3206, 3249 and 3385 cm(-1). Raman spectroscopy coupled with infrared spectroscopy has enabled aspects about the molecular structure of the borate mineral ameghinite to be assessed.