Guallatiri has erupted andesite, dacite and rhyolite, with dacite dominating. Pyroxene andesites are found up to of altitude. Analysis of lava at Domo Tinto lava dome has indicated that phenocrysts include amphibole, biotite, pyroxene and some apatite. Mafic inclusions have also been found in Domo Tinto rocks. The Domo Tinto eruption may have been triggered by the injection of basaltic andesite into two magma chambers containing crystalline andesite. Native deposits of sulfur are also found and sulfur is the most common mineral in fumarolic deposits; but arsenic, boron, calcium and silicon are also found. Such fumarolic deposits at Guallatiri and the other Andean volcano Lastarria aside from pure sulfur also consist of anhydrite, auripigment, baryte, burkeite, cristobalite, galena, gypsum, magnetite, pyrite, quartz and sassolite.