A number of xenoliths occur in Lascar's rocks; a large amount of the phenocrysts are ultimately derived from them. Hornfels, skarn, and rocks that are part of Lascar's lava dome ridge are the source of these xenoliths. Minerals encountered in xenoliths include andradite, anhydrite, anorthite, apatite, biotite, calcite, diopside, fassaite, garnet, gypsum, ilmenite, magnetite, monazite, orthopyroxene, perovskite, plagioclase, prehnite, quartz, sphene, thorite, wilkeite, wollastonite and zircon. A number of such xenoliths formed from carbonate rocks that were influenced by magma of Lascar and of other volcanoes such as Tumisa.