Micro-Raman spectroscopy of thaumasite

Micro-Raman spectroscopy can be used to identify thaumasite. Three mineral samples were studied; in addition to the peaks at 658 and 990 cm(-1) previo usly reported by Bensted and Varma (assigned to SiO6 and SO4 nu (1) stretch ing, respectively), further peaks were found, which we assign to carbonate (1072 cm(-1)) and hydroxide/water (in the region of 3300 cm(-1)) species. T haumasite lost no water at 100 degreesC even after prolonged heating, howev er, most of the water was lost after heating at 110 degreesC for 10 min. Si multaneously, the sharp peaks due to sulfate and carbonate groups (990 and 1072 cm(-1)) disappeared and were replaced by much broader peaks (1002 and 1082 cm(-1)). However, for the peak at 658 cm(-1) attributed to silicate, t here was no clear replacement. Further changes were evident in the vibratio ns of sulfate species. Thaumasite in veins was readily distinguished from e ttringite in two specimens of field concrete, based on the combination of p eaks at 658, 990, and 1072 cm(-1), with spatial resolution of approximately 50 mum (C) 2001 Elsevier Science Ltd. All rights reserved.