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Andesite lava flow USGSAndesite is an intermediate extruisve lava with 52-63%silica content. It conatins Plagioclase feldspar,pyroxenes and hornblende , it may also contain smaller quantitiies or biotite and hornblende. It has a dark grey appearence and like most lavas it has small crystals.Phenocrysts ( large crystals formed already in the melt) are present. Gas vesicles called amygdales are often filled wit a mineral called zeolite.Andesite is named after the Andes mountain range in South America where it is a common volcanic lava. Andesite occurs as long lava flows from Stratovolcanoes in subdction zone settings.It erupts between 900 C and 1100 C a similar temperature to basalt but much higher than Rhyollite.