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 these felsic sequences and dating their time of formation, stratigraphic units of different locations can be correlated despite the obstacles or discontinuity in between felsic volcanic units. The geochronology of Archean events strongly relies on U-Pb dating and Lu-Hf dating. Since mafic rocks (contain low silica content, such as basalt) are lack of zircon, only the age of felsic rocks can be dated among the volcanic rocks in greenstone belts. As felsic volcanic rocks are episodically deposited in between mafic layers, the age range of a particular mafic layer can be constrained by the upper and lower felsic volcanic layers.