Raman spectroscopic study of the arsenite minerals ludlockite Pb Fe43+As10O22 and schneiderhöhnite Fe2+Fe33+As53+O6

Raman spectroscopy has been used to study the two arsenite minerals ludlockite and schneiderhöhnite, which have a common structural unit of pentameric arsenite groups. Raman bands for ludlockite are observed at 666, 674, 743, 756 and 798 cm−1 and for schneiderhöhnite at 685, 719, 739, 774 and 798 cm−1. Based upon DFT calculations, the band at 798 cm−1 is attributed to ν1 AsO32− symmetric stretching vibration. Raman bands at 743 and 756 cm−1 for ludlockite and at 719 and 739 cm−1 for schneiderhöhnite are assigned to the ν3 AsO32− antisymmetric stretching vibration. Even though the minerals are very dark coloured to black in appearance, successful Raman spectra were collected.