Lava Vesuvius between May 14 and June 4, 1737. Serao described "a flow of fiery lava" as an analogy to the flow of water and mud down the flanks of the volcano following heavy rain. The composition of almost all lava of the Earth's crust is dominated by silicate minerals, mostly feldspars, olivine, pyroxenes, amphiboles, micas and quartz. Igneous rocks, which form lava flows when erupted, can be classified into three chemical types: "felsic", "intermediate", and "mafic" (four if one includes the super-heated "ultramafic"). These classes are primarily chemical, however, the chemistry of lava also tends to correlate with the magma
Archean felsic volcanic rocks from 62 to 78 wt% in rock. In terms of mineralogy, the felsic volcanic rocks are rich in feldspar and quartz. A typical mineral assemblage is quartz + feldspar (albite/oligoclase) + amphibole (chlorite) + micas (biotite and/or muscovite). The mineralogy seems similar with modern rhyolites and dacites. The volcanics are aphanitic, whereas some exhibits porphyritic texture that certain larger minerals (phenocrysts) are visible by eyes. Felsic volcanic rocks also include felsic tuff that was formed when tephra was consolidated. Tuff is composed of volcanic ash, glass shards and lithic fragments. Reported eutaxitic tuff from Superior Province, Canada (Figure 3), contains