Most mafic rocks found are 55% SiO2 basaltic andesites. The sheeted dykes show a general tholeiitic trend, of basalts, andesites and dacites. In general, these are calc-alkali basalts, basaltic andesites, and andesites. From diabases, basalts, andesites and other igneous rocks a third type of hornfels is produced. The rocks are mostly dacites and andesites. Pyroxene andesites are found up to of altitude. The rocks were mainly igneous in nature, including granites, andesites, dacites, rhyolites, mafic dykes, etc. Lau Basin volcanics are mainly andesites and dacites that were erupted 6.4 to 9.0 Ma. Classification of andesites may be refined according to the most abundant phenocryst. Andesites from the old cone are classified as hornblende and pyroxene andesites. The oldest exposed rocks within the belt are fine to medium-grained basalts and andesites. High-magnesium andesites in island arcs may be primitive andesites, generated from metasomatized mantle. The discovery of andesites shows that some Martian rocks have been remelted and reprocessed. Also in the early Miocene more intermediate Basaltic andesites occur along faults and in grabens. The results indicated that "Barnacle Bill" is much like Earth's andesites, confirming past volcanic activity.