Vibrational Spectroscopy of the Borate Mineral Priceite—Implications for the Molecular Structure

Abstract

Priceite is a calcium borate mineral and occurs as white crystals in the monoclinic pyramidal crystal system. We have used a combination of Raman spectroscopy with complimentary infrared spectroscopy and scanning electron microscopy with Energy-dispersive X-ray Spectroscopy (EDS) to study the mineral priceite. Chemical analysis shows a pure phase consisting of B and Ca only. Raman bands at 956, 974, 991, and 1019 cm À1 are assigned to the BO stretching vibration of the B 10 O 19 units. Raman bands at 1071, 1100, 1127, 1169, and 1211 cm À1 are attributed to the BOH in-plane bending modes. The intense infrared band at 805 cm À1 is assigned to the trigonal borate stretching modes. The Raman band at 674 cm À1 together with bands at 689, 697, 736, and 602 cm À1 are assigned to the trigonal and tetrahedral borate bending modes. Raman spectroscopy in the hydroxyl stretching region shows a series of bands with intense Raman band at 3555 cm À1 with a distinct shoulder at 3568 cm À1 . Other bands in this spectral region are found at 3221, 3385, 3404, 3496, and 3510 cm À1 . All of these bands are assigned to water stretching vibrations. The observation of multiple bands supports the concept of water being in different molecular environments in the structure of priceite. The molecular structure of a natural priceite has been assessed using vibrational spectroscopy.