Subrounded forms are commonly of juvenile origin, but explosively broken cognate and accidental fragments may become rounded by repeated extrusion and fallback into a vent before final ejection. Armored lapilli form when wet ash becomes plastered around a solid nucleus such as crystal, pumice or lithic fragments during a hydrovolcanic eruption. Blocks are angular to sub-angular fragments of juvenile, cognate and accidental origin derived from extrusion of lava such as in domes, or from the edifice of the volcano or from its basement. Volcanic breccia applies to all volcaniclastic rocks composed predominantly of angular volcanic particles greater than 2 mm in size. Bombs are thrown from vents in a partly molten condition and solidify during flight or shortly after they land.
Bombs are therefore almost exclusively juvenile.
Molten clots are shaped by drag forces during flight, and if still plastic, their shape can be modified by impact when they hit the ground. They are most commonly produced from magma of intermediate and silicic compositions. Basaltic bombs usually show little surface cracking, although some may have fine cracks caused by stretching of a thin, glassy surface over a still- plastic interior upon impact. Cauliflower bombs have cauliflower shapes with dense to vesicular interiors because of quick-quenching in aqueous environments. They are formed in hydrovolcanic eruptions.