I need to run a supervised classification on ASTER data in order to map a rock formation, which is composed of chert. There is no shortage of indices which can be used to highlight silica rich formations, see http://www.ga.gov.au/image_cache/GA7833.pdf. However, all of the indices I have found thus far utilize the TIR bands, which have a spatial resolution of 90m, and I need to map at a much finer scale than this permits. The either of the the 30m and 15m resolutions of SWIR and VNIR respectively should suffice. The problem is that I can't find any silica indices which use these bands. I understand that any such indices might be sub optimal in comparison to those which use the TIR bands, but in this case resolution is of uptmost importance. So, the question is; does anyone know of any established chert/silica indices which use the VNIR or SWIR bands?