- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of Geology Exclusive of North America, Geological Society of America, Boulder, CO, United States
Of the three mineral pairs garnet-biotite, garnet-hornblende, and garnet-pyroxene, selected for study of the distribution of the elements Mg, Fe, Mn, and Ca in the search for a method of determining metamorphic grade, the results obtained with the first two pairs are reported. The approach is described and results are tabulated for garnet and biotite in 38 rock samples from widely distributed localities and for garnet and hornblende in 20 specimens. It is shown that metamorphic grade can be estimated from atomic ratios and the formulas are given.