lapillituffen

Lapillituffen, or lapilli tuff, is a type of pyroclastic rock characterized by a substantial content of lapilli-sized tephra fragments (roughly 2–64 mm) held together by a finer matrix of volcanic ash and other cementing material. The rock forms when explosive volcanic ejecta consisting of lapilli and finer ash settles from an eruption plume or is deposited by pyroclastic flows, then lithifies through diagenesis or welding.

Composition and texture: The coarse fraction is dominated by lapilli, which may be glassy, crystalline, or lithic in origin. The matrix is typically fine-grained ash, with cementing materials such as silica, clays, or carbonate binding the particles. Welding, when present, occurs in hotter, denser flows and produces a denser, more cohesive rock; non-welded lapilli tuffs are usually more friable.

Classification: The name lapilli tuff is used when lapilli constitute the principal coarse component of the rock. If the deposit shows significant welding, a welded lapilli tuff designation may be used. The overall chemical composition can range from felsic to intermediate, reflecting the source magma of the eruption.

Occurrence and significance: Lapillituffs are widespread in volcanic regions and record explosive eruption activity, including tephra fall and pyroclastic flow events. They aid in interpreting eruption styles, depositional environments, and the eruptive history of volcanic fields.