Raman and infrared spectroscopic characterization of the arsenate‐bearing mineral tangdanite– and in comparison with the discredited mineral clinotyrolite

Abstract

The minerals clinotyrolite and fuxiaotuite are discredited in terms of the mineral tangdanite. The mixed anion mineral tangdanite Ca 2 Cu 9 (AsO 4 ) 4 (SO 4 ) 0.5 (OH) 9 9H 2 O has been studied using a combination of Raman and infrared spectroscopy. Characteristic bands associated with arsenate, sulphate and hydroxyl units are identified. Broad bands in the OH stretching region are observed and are resolved into component bands. These bands are assigned to water and hydroxyl stretching vibrations. Two intense Raman bands at 837 and approximately 734 cm À1 are assigned to the ν 1 (AsO 4 ) 3À symmetric stretching and ν 3 (AsO 4 ) 3À antisymmetric stretching modes. Infrared bands at 1023 cm À1 are assigned to the (SO 4 ) 2À ν 1 symmetric stretching mode, and infrared bands at 1052, 1110 and 1132 cm À1 assigned to (SO 4 ) 2À ν 3 antisymmetric stretching modes, confirming the presence of the sulphate anion in the tangdanite structure. Raman bands at 593 and 628 cm À1 are attributed to the (SO 4 ) 2À ν 4 bending modes. Low-intensity Raman bands found at 457 and 472 cm À1 are assigned to the (AsO 4 ) 3À ν 2 bending modes. A comparison is made with the previously obtained spectral data on the discredited mineral clinotyrolite.

Penberthycroftite, [Al6(AsO4)3(OH)9(H2O)5]·8H2O, a second new hydrated aluminium arsenate mineral from the Penberthy Croft mine, St. Hilary, Cornwall, UK

“…In the region for As-O stretching vibrations, 700-900 cm -1 (Vansant et al, 1973), two doublets are observed, with main peaks at 855 and 795 cm -1 and shoulders at 884 and 775 cm -1 . Similar doublets were reported by Frost et al (2015) for the arsenate mineral tangdanite. They assigned the higher wavenumber doublet to ν1 symmetric stretching and the lower wavenumber doublet to ν3 antisymmetric stretching vibrations.…”

Aquaphotomics monitoring of strawberry fruit during cold storage – A comparison of two cooling systems

“…The behavior of absorbance at band 1,503 nm is common for both storage conditions; there is a sharp, strong increase in absorbance immediately upon the storage. There are many reports about this particular band in characterization of minerals and attributed to vibrational mode of hydrous defects in the crystal structure (90)(91)(92)(93)(94)(95)(96). In analogy to these reports, the absorbance at this band can be considered as indicator of shallow, superficial, surface damage, and small openings in the structure of materials that enhance exposure to the environment.…”

Recent advances in linear and non‐linear Raman spectroscopy. Part X

“…[115] D'Ippolito and co-workers elucidate the unique Raman fingerprint of chromate, aluminate and ferrite spinels. [116] Frost and co-workers characterized Raman and infrared spectra of the arsenate-bearing mineral tangdanite, and in comparison with the discredited mineral clinotyrolite [117] Golovin et al carried out in situ ambient and high-temperature Raman spectroscopic studies of nyerereite (Na,K) 2 Ca(CO 3 ) 2 and posed the question can hexagonal zemkorite be stable at earth-surface conditions? They conclude that they do not expect to find zemkorite in any magmatic, metasomatic or hydrothermal rocks exposed at the Earth's surface.…”