Sample F20: Hornblende Andesite
Amphibole (hornblende) and plagioclase phenocrysts set in a sub-trachytic
groundmass (note how the plagioclase laths in the groundmass appear to "flow"
around the phenocrysts). The basal sections of the hornblende phenocrysts
show the characteristic 120˚/60˚ cleavage angles characteristic of amphibole.