Andesite

Andesite

Igneous rock
Photomicrograph of andesite in thin section (between crossed polars)
Composition
Intermediate Major minerals: plagioclase (often andesine) and pyroxene or hornblende Accessory minerals: magnetites, biotite, sphene, quartz

Intermediate
Major minerals: plagioclase (often andesine) and pyroxene or hornblende

Andesite (pronunciation: /ˈændᵻsaɪt/ or /ˈændᵻzaɪt/) is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite, and ranges from 57 to 63% silicon dioxide (SiO₂) as illustrated in TAS diagrams. The mineral assemblage is typically dominated by plagioclase plus pyroxene or hornblende. Magnetite, zircon, apatite, ilmenite, biotite, and garnet are common accessory minerals.Alkali feldspar may be present in minor amounts. The quartz-feldspar abundances in andesite and other volcanic rocks are illustrated in QAPF diagrams.