Rock cycle called intrusive or plutonic and cools very slowly, producing a coarse-grained texture such as the rock granite. As a result of volcanic activity, magma (which is called lava when it reaches Earth's surface) may cool very rapidly while being on the Earth's surface exposed to the atmosphere and are called extrusive or volcanic rocks. These rocks are fine-grained and sometimes cool so rapidly that no crystals can form and result in a natural glass, such as obsidian, however the most common fine grained rock would be known as basalt. Any of the three main types of rocks (igneous, sedimentary, and
Breccia two classes: Volcanic pyroclastic rocks are formed by explosive eruption of lava and any rocks which are entrained within the eruptive column. This may include rocks plucked off the wall of the magma conduit, or physically picked up by the ensuing pyroclastic surge. Lavas, especially rhyolite and dacite flows, tend to form clastic volcanic rocks by a process known as "autobrecciation". This occurs when the thick, nearly solid lava breaks up into blocks and these blocks are then reincorporated into the lava flow again and mixed in with the remaining liquid magma. The resulting breccia is uniform in rock type