SHORT COMMUNICAT IONS 25I REFERENCES

Biotites in calc-alkaline intrusive rocks F o L L O W I N G the initial work of Heinrich (t 946), Foster (t 960) examined the relation-ships between biotite compositions and generalized geological occurrences. She found that biotites from varieties of calc-alkaline intrusive rocks show considerable overlap when the Y site cations are plotted on triangular diagrams with (AF i, Fe 3+, Ti4+), (Fe 2+, Mn~+), and Mg 2+ as apices, indicating that no simple correlation between biotite composition and host-rock types exists. However, Foster suggested that this overlap, in part, may be due to the loose usage of rock names uch as 'granite'. The objects of this study are to revise Foster's diagram especially for intrusive calc-alkaline rocks using a rigorous rock classification and to test if the conclusions reached by the previous tudy are substantiated. Analyses of biotites from calc-alkaline rocks were selected from the literature (sources quoted in the list of references) on the following criteria: a mode of the host rock was available; the rock was substantially free of metamorphism, weathering, and hydrothermal teration. These criteria, especially the first, meant the rejection o