Compositional relations of coexisting orthopyroxene, pigeonite and augite in a tholeiitic andesite from Hakone Volcano

摘要: The compositions of five different coexisting pyroxenes hypersthene, pigeonite and augite in groundmass bronzite phenocryst a tholeiitic andesite from Hakone Volcano, Japan have been determined by the electron probe microanalyser. It is shown that there compositional gap about 25 mole per cent CaSiO3 between augite, compared with 35 phenocrystic bronzite. Subcalcic or pigeonitic was not found. which occurs only as thin rims less calcic more iron-rich than augite. also 3–4 CaSiO3-rich hypersthene. Fe/(Mg + Fe) ratios these hypersthene are 0.31 0.33, respectively. suggested results continuous solid solution does exist ratio at least near 0.3 under conditions crystallization andesite. Mg-Fe partition textural relation crystallized liquid crystallized.