WEATHERING DETECTED BY RAMAN-SPECTROSCOPY USING AL-ORDERING IN ALBITE

Albite samples from Ontario, Canada, laboratory weathered in HCl solut ions at pH 1 have been analysed and compared to unreacted mineral samp les with the same crystal orientation using Raman microspectrometry. T he study was focused on Raman bands reflecting ill-ordering because de stabilisation of Al-O bonds with subsequent release of Al is well reco gnised to be a major factor in low pH dissolution of albite. Analyses of unweathered samples reveal that most bands in the albite spectra sh ow variations in intensities for different crystal orientations in the wavenumber range 100 to 1200 cm(-1). A well-defined crystal orientati on is therefore essential to a successful investigation of weathered s amples. Unweathered albite has two bands; 455 and 976 cm(-1) in the sp ectrum normal to the (001) face, which have been related to A-ordering in the structure. In spectra of weathered albite crystals, with the s ame orientation, the band most sensitive to alteration is 976 cm(-1). This band is very strong for unreacted albite, but diminishes in inten sity relative to the other bands at the initial stage cm of weathering . When dissolution continued, the structural information in the range 700 to 1200 cm(-1) was completely lost, shown as a bandbroadening of a less organised structure, while the characteristic albite bands still could be observed in the range 100 to 600 cm(-1). (C) 1998 Elsevier S cience B.V. All rights reserved.