PROBE-AMPH - A SPREADSHEET PROGRAM TO CLASSIFY MICROPROBE-DERIVED AMPHIBOLE ANALYSES

A Microsoft Excel(TM) spreadsheet program has been developed to calcul ate structural formulae of microprobe-derived amphibole analyses and d etermine classification parameters according to the International Mine ralogical Association scheme for amphibole nomenclature. The program h as been tested in the determination of formulae and classification of 138 amphibole analyses from the literature. Of these, the small percen tage (14%) of discrepancies were determined mainly to be the result of (i) differences between measured (wet chemical) and estimated values for FeO and Fe2O3 and (ii) differences inherent in summing structural formula of microprobe data to 23 oxygens and wet chemical data to 24 o xygens. The program has been developed for the Apple Macintosh but a P C version also is available. Spreadsheet implementations of four publi shed geobarometers based on the total aluminium content of certain cal cic amphiboles also are presented. These geobarometers are applicable to metaluminous plutonic (and associated volcanic) rocks containing th e assemblage iotite-quartz-plagioclase-(orthoclase)-sphene-FeTi oxides and apply to a pressure range of 2.5-13 kbar.