 Each ignimbrite has usually a uniform composition but there is some variation between individual ignimbrites; for example older rocks contain amphibole and younger rocks instead sanidine.Minerals contained in the eruption products include allanite, apatite, biotite, hornblende, ilmenite, magnetite, orthopyroxene, plagioclase, quartz, sanidine and zircon.Hydrothermal alteration has left calcite in some rocks.