What Is Volcanic Rock？

Volcanic rocks refer to rocks formed by the condensation of hot magma from deep Earth's surface through volcanic vents, which can be divided into narrow volcanic rocks and broad volcanic rocks.

Narrowly defined, volcanic rock refers to volcanic lava, which is a type of low viscosity, low volatile magma (such as basic magma) that flows out of a volcano in the form of a melt. In the late stage of a volcanic eruption, some high viscosity acidic magma can also form lava when a large amount of volatile matter in the magma chamber escapes and invades the surface.

The composition of magma is different, and the rocks formed after cooling and solidification are also different. The basic extrusive rocks are basalt, the neutral extrusive rocks are andesite, the acidic extrusive rocks are rhyolite, and the semi alkaline and alkaline extrusive rocks are trachyte and phonolite.

The ejected rocks often have structures such as pores, almonds, and flow patterns, and are mostly composed of glassy, cryptocrystalline, or porphyritic structures. Glassy obsidian, perlite, turquoise, pumice, and other eruptive rocks are called volcanic glassy rocks.

In a broad sense, volcanic rocks include not only lava but also pyroclastic rocks. Volcanic clastic rocks are mainly acidic rocks with high viscosity and high volatile content that will erupt to the surface through explosive eruptions, often mixed with a certain amount of normal sediment or lava material.