Raman spectroscopy of the basic copper arsenate mineral: euchroite

Raman spectroscopy complemented with infrared spectroscopy was used to study the molecular structure of the mineral euchroite, a mineral involved in a complex set of equilibria between the copper hydroxy arsenates: euchroite Cu(2)(AsO(4))(OH)center dot 3H(2)O -> olivenite Cu(2)(AsO(4))(OH) -> strashimirite Cu(8)(AsO(4))(4)(OH)(4)center dot 5H(2)O -> arhbarite Cu(2)Mg(AsO(4))(OH)(3). The Raman bands observed at 848 and 768 cm(-1) are assigned to the nu(1) and nu(3) (AsO(4))(3-) stretching vibrations. Two Raman bands at 358 and 385 cm(-1) are attributed to the nu(2) (AsO(4))(3-) bending mode and two Raman bands at 441 and 474 cm(-1) to the nu(4) AsO(4)(3-) bending modes. Two sharp Raman bands are observed at 3470 and 3537 cm(-1) and are attributed to the stretching vibrations of hydroxyl units. A comparison of the Raman spectrum of euchroite is made with the other copper hydroxy arsenate minerals including strashimirite, olivenite, cornubite, and cornwallite. Copyright (C) 2009 John Wiley & Sons, Ltd.