pyroclastite

Pyroclastite is a general term for a rock composed of fragments of volcanic material, called pyroclasts, that have been ejected during a volcanic eruption and subsequently consolidated. These pyroclasts can vary greatly in size, from fine ash to large volcanic bombs. The composition of pyroclastites reflects the source rock and the eruptive process, and they can include fragments of existing volcanic rocks, fresh magma, and mineral crystals.

The formation of pyroclastites involves the fragmentation of magma or solid rock during explosive volcanic events. This fragmentation can occur due to rapid depressurization of magma, the interaction of magma with water (phreatomagmatic eruptions), or the forceful expulsion of solid rock. Once ejected, these fragments fall to the ground, where they can accumulate and eventually become lithified into solid rock through processes like compaction, cementation, and recrystallization.

Pyroclastites are classified based on the size of their constituent pyroclasts. Tuff is a pyroclastite composed primarily of volcanic ash, which are particles less than 2 millimeters in diameter. Lapilli are pyroclasts ranging from 2 to 64 millimeters, and agglomerates or breccias are composed of larger fragments, often exceeding 64 millimeters. The specific type and characteristics of a pyroclastite can provide valuable information about the nature and intensity of past volcanic eruptions.