Volcanic bomb most of the damage they cause is from impact, or subsequent fire damage. Bomb explosions are most often observed in "bread-crust" type bombs. Bombs are named according to their shape, which is determined by the fluidity of the magma from which they are formed. Volcanic bomb A volcanic bomb is a mass of molten rock (tephra) larger than 64 mm (2.5 inches) in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. They cool into solid fragments before they reach the ground. Because volcanic bombs cool after they leave the volcano, they are extrusive igneous rocks.
Pitchstone Pitchstone Pitchstone is a dull black glassy volcanic rock formed when felsic lava or magma cools quickly. It is similar to obsidian but is defined by the International Union of Geological Sciences as having a higher water content. It is a volcanic glass; however, unlike a glass, pitchstone has an irregular hackly fracture not a conchoidal fracture. That is due to its coarser (than obsidian) crystal structure. Pitchstone has a resinous lustre, or silky in some cases, and a variable composition. Its colour may be mottled, streaked, or uniform brown, red, green, gray, or black. It is an extrusive rock