A Raman and infrared spectroscopic analysis of the phosphate mineral wardite NaAl3(PO4)2(OH)4 .2(H2O) from Brazil.
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2014
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A wardite mineral sample from Lavra Da Ilha, Minas Gerais, Brazil has been examined by vibrational spectroscopy. The mineral is unusual in that it belongs to a unique symmetry class, namely the tetragonal-trapezohedral group. The structure of wardite contains layers of corner-linked –OH bridged MO6 octahedra stacked along the tetragonal C-axis in a four-layer sequence and linked by PO4 groups. Consequentially not all phosphate units are identical. Two intense Raman bands observed at 995 and 1051 cm^-1 are assigned to the m1 PO4^3- symmetric stretching mode. Intense Raman bands are observed at 605 and 618 cm^-1 with shoulders at 578 and 589 cm^-1 are assigned to the m4 out of plane bending modes of the PO4^3- . The observation of multiple bands supports the concept of non-equivalent phosphate units in the structure. Sharp infrared bands are observed at 3544 and 3611 cm^-1 are attributed to the OH stretching vibrations of the hydroxyl units. Vibrational spectroscopy enables subtle details of the molecular structure of wardite to be determined.
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Wardite, Cyrilovite, Phosphate, Hydroxyl, Raman spectroscopy
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FROST, RAY L. et al. A Raman and infrared spectroscopic analysis of the phosphate mineral wardite NaAl3(PO4)2(OH)4 .2(H2O) from Brazi. Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy, v. 11, p. 1, 2014. Disponível em: <http://www.sciencedirect.com/science/article/pii/S1386142514001942>. Acesso em: 04 set. 2014.