According to Meyer-Abich (1956) Santa Ana volcano lavas are composed dominantly of olivine-pyroxene basalts and hypersthene andesites. Carr and Pointier (1981) describe Santa Ana andesites as "porphyritic, pilotaxitic with unzoned to normally zoned phenocrysts of plagioclase and pyroxene" while the basalts show evidences for disequillibrium such as intensely resorbed zones within the margins of plagioclase and clinopyroxene phenocrysts. Zoned plagioclase phenocrysts show evidence of bimodal composition.
Chemical composition of Santa Ana lavas suggest that several magmatic processes have occured, including magma mixing, crystal fractionation and magma stratification (Carr and Pointier, 1981). These results also suggest the existence of two separate superficial magma bodies perhaps connected to a deeper main magma chamber beneath Santa Ana and Izalco volcanoes.
Cox-Bell-Pank, (1979) diagram showing different rock types for some Santa Ana samples.