Andrés Lópes

Raman and infrared spectroscopic characterization of the phosphate mineral paravauxite Fe2+Al2(PO4)2(OH)2⋅8H2O

We have undertaken a vibrational spectroscopic study of paravauxite the Siglo XX mine, Bustillo Province, northern of Potosí department, Bolivia. This mine is important source for rare and unusual secondary phosphate minerals and is the type locality for a number of rare phosphates such as vauxite, sigloite, metavauxite and for jeanbandyite. The chemical formula of the studied sample was determined as Fe(2+)(0.9)5, Al(0.07)Σ1.02 (Al)2.09 (PO4)1:97 (OH)1.98 · 7.90(H2O). The Raman spectrum is dominated by an intense Raman band at 1020 cm(-1) assigned to the PO4(3-) ν1 symmetric stretching mode. Low intensity Raman bands found at 1058, 1115 and 1148 cm(-1) are assigned to the PO4(3-) ν3 antisymmetric stretching vibrations. Raman bands of paravauxite at 537, 570, 609 and 643 cm(-1) are assigned to the ν4 PO4(3-) bending modes whilst the Raman bands at 393 and 420 cm(-1) are due to the ν2 PO4(3-) bending modes. The Raman spectral profile of paravauxite in the hydroxyl stretching region is broad with component bands resolved at 3086, 3215, 3315, 3421, 3505 and 3648 cm(-1). Vibrational spectroscopy enables the assessment of the molecular structure of paravauxite to be undertaken.

A Vibrational Spectroscopic Study of the Silicate Mineral Kornerupine

We have studied the mineral kornerupine, a borosilicate mineral, by using a combination of scanning electron microscopy with energy-dispersive analysis and Raman and infrared spectroscopy. Qualitative chemical analysis of kornerupine shows a magnesium–aluminum silicate. Strong Raman bands at 925, 995, and 1051 cm−1 with bands of lesser intensity at 1035 and 1084 cm−1 are assigned to the silicon–oxygen stretching vibrations of the siloxane units. Raman bands at 923 and 947 cm−1 are attributed to the symmetrical stretching vibrations of trigonal boron. Infrared spectra show greater complexity and the infrared bands are more difficult to assign. Two intense Raman bands at 3547 and 3612 cm−1 are assigned to the stretching vibrations of hydroxyl units. The infrared bands are observed at 3544 and 3610 cm−1. Water is also identified in the spectra of kornerupine.

Vibrational spectroscopy of the borate mineral gaudefroyite Ca4Mn3-x3+(BO3)3(CO3)(O,OH) from N’Chwaning II mine, Kalahari, Republic of South Africa

Gaudefroyite Ca4MN3+3-x (BO3)3(CO3) (O, OH)3 is an unusual mineral containing both borate and carbonate groups and is found in the oxidation zones of manganese minerals, and it is black in color. Vibrational spectroscopy has been used to explore the molecular structure of gaudefroyite. Gaudefroyite crystals are short dipyramidal or prismatic with prominent pyramidal terminations, to 5 cm. Two very sharp Raman bands at 927 and 1076 cm(-1) are assigned to trigonal borate and carbonate respectively. Broad Raman bands at 1194, 1219 and 1281 cm(-1) are attributed to BOH in-plane bending modes. Raman bands at 649 and 670 cm(-1) are assigned to the bending modes of trigonal and tetrahedral boron. Infrared spectroscopy supports these band assignments. Raman bands in the OH stretching region are of a low intensity. The combination of Raman and infrared spectroscopy enables the assessment of the molecular structure of gaudefroyite to be made.

Infrared and Raman Spectroscopic Characterization of the Silicate Mineral Gilalite Cu5Si6O17 · 7H2O

ABSTRACT Gilalite is a copper silicate mineral with a general formula of Cu5Si6O17 · 7H2O. The mineral is often found in association with another copper silicate mineral, apachite, Cu9Si10O29 · 11H2O. Raman and infrared spectroscopy have been used to characterize the molecular structure of gilalite. The structure of the mineral shows disorder, which is reflected in the difficulty of obtaining quality Raman spectra. Raman spectroscopy clearly shows the absence of OH units in the gilalite structure. Intense Raman bands are observed at 1066, 1083, and 1160 cm−1. The Raman band at 853 cm−1 is assigned to the –SiO3 symmetrical stretching vibration and the low-intensity Raman bands at 914, 953, and 964 cm−1 may be ascribed to the antisymmetric SiO stretching vibrations. An intense Raman band at 673 cm−1 with a shoulder at 663 cm−1 is assigned to the ν4 Si-O-Si bending modes. Raman spectroscopy complemented with infrared spectroscopy enabled a better understanding of the molecular structure of gilalite.

Infrared and Raman spectroscopic characterization of the arsenate mineral ceruleite Cu2Al7(AsO4)4(OH)13· 11.5(H2O).

The molecular structure of the arsenate mineral ceruleite has been assessed using a combination of Raman and infrared spectroscopy. The most intense band observed at 903 cm(-1) is assigned to the (AsO4)(3-) symmetric stretching vibrational mode. The infrared spectrum shows intense bands at 787, 827 and 886 cm(-1), ascribed to the triply degenerate ν3 antisymmetric stretching vibration. Raman bands observed at 373, 400, 417 and 430 cm(-1) are attributed to the ν2 vibrational mode. Three broad bands for ceruleite found at 3056, 3198 and 3384 cm(-1) are assigned to water OH stretching bands. By using a Libowitzky empirical equation, hydrogen bond distances of 2.65 and 2.75Å are calculated. Vibrational spectra enable the molecular structure of the ceruleite mineral to be determined and whilst similarities exist in the spectral patterns with the roselite mineral group, sufficient differences exist to be able to determine the identification of the minerals.