Unlike the vesicular and aphyric pyroclastic rock at Glass Mountain and Little Glass Mountain, lava deposits from the Chaos Crags are porphyritic with average vesicularity values at about 30%. Most of these vesicles exhibit oval shapes. Pumice from the eruption has high phenocryst content, with crystals of plagioclase, hornblende, biotite, quartz, and magnetite; it also has low vesicularity values.