Lapilli are spheroid, teardrop, dumbbell or button-shaped droplets of molten or semi-molten lava ejected from a volcanic eruption which fall to earth while still at least partially molten. These granules are not accretionary, but are the direct result of liquid rock cooling as it travels through the air.

Lapilli tuffs are a very common form of volcanic rock typical of rhyolite, andesite and dacite. welding of semi-molten lapilli into what is known as a welded tuff. pyroclastic eruptions. Large thicknesses of lapilli can be deposited during a basal surge eruption. Most lapilli tuffs which remain in ancient terrains are formed by the accumulation and

The heat of the newly-deposited volcanic pile tends to cause the semi-molten material to flatten out as they become welded. Welded tuff textures are distinctive (termed eutaxitic), with flattened lapilli, fiamme, blocks and bombs forming oblate to discus-shaped forms within layers. These rocks are quite indurated and tough, as opposed to non-welded lapilli tuffs which are unconsolidated and easily eroded.