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)·3H 2 O → olivenite Cu 2 (AsO 4 )(OH) → strashimirite Cu 8 (AsO 4 ) 4 (OH) 4 ·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 ν 1 and ν 3 (AsO 4 ) 3− stretching vibrations. Two Raman bands at 358 and 385 cm −1 are attributed to the ν 2 (AsO 4 ) 3− bending mode and two Raman bands at 441 and 474 cm −1 to the ν 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 © 2009 John Wiley & Sons, Ltd.