Phenocrystic olivines in the basalts and andesites
range in composition from cores of 6.3 and Foes 2
to rims of Fosa.2 and Fos2.3 respectively,and euhedral
olivine in diopside megacrysts from the andesite
is Fos7.3 On the other hand, groundmass olivines
in basalts are Fos6.ato Fo7s.5 All the olivines
are characterized by very high Fo contents and a
narrow compositional range, regardless of their
occunence and bulk rock composition (Fig. 6)