The volcano erupted comendite, hawaiite and mugearite, with the former found at Chang Peak and the latter two at Mount Waesche proper; the parasitic cones have erupted a mugearite-benmoreite succession. The occurrence of rhyolite has also been reported. Phenocrysts at Chang Peak include aenigmatite, alkali feldspar, ilmenite and quartz and at Mount Waesche olivine, plagioclase and titanaugite. Granulite and pyroxenite xenoliths have also been found. Despite their proximity, Mount Sidley and Mount Waesche have erupted distinctly different rocks. Unusually for volcanoes in Marie Byrd Land, the chemistry of volcanic rocks at Mount Waesche appears to have changed over time.