Whelanite Ca₅Cu₂(OH)₂CO₃,Si₆O₁₇·4H₂O--a vibrational spectroscopic study.

Whelanite Ca(5)Cu(2)(OH)(2)CO(3),Si(6)O(17)·4H(2)O is a hydrated hydroxy mixed anion compound with both silicate and carbonate anions in the formula. The structural characterisation of the mineral whelanite remains incomplete. Whelanite is probably a neosilicate with Cu(2+) in square planar coordination. Two Raman bands at 1070 and 1094 cm(-1) are assigned to the ν(1) symmetric stretching modes of the CO(3)(2-) units. The observation of two symmetric stretching modes supports the concept of two non-equivalent CO(3)(2-) units in the whelanite structure. The intense sharp Raman band at 1006 cm(-1) is assigned to the ν(1) (A(1g)) symmetric stretching vibration of the Si(6)O(17) units. The splitting of the ν(3) vibrational mode offers support to the concept that the SiO(4) tetrahedron in whelanite is strongly distorted. A very intense Raman band observed at 666 cm(-1) with a shoulder at 697 cm(-1) is assigned to the ν(4) vibrational modes. Intense Raman bands at 3534, 3556, 3550 and 3595 cm(-1) are assigned to the stretching vibrations of the OH units. Low intensity Raman bands at 2910, 3187 and 3453 cm(-1) are assigned to water stretching modes. Thus, vibrational spectroscopy has been used to characterise the molecular structure of whelanite. Whelanite is a mineral that could be conceived as a healing mineral.