Editing Lapilli (section)

==Formation==
Lapilli are spheroid-, teardrop-, dumbbell- or button-shaped droplets of molten or semi-molten [[lava]] ejected from a volcanic eruption that fall to earth while still at least partially molten. These granules are the direct result of liquid rock cooling as it travels through the air.

Lapilli [[tuff]]s are a very common form of volcanic rock typical of [[rhyolite]], [[andesite]] and [[dacite]] pyroclastic eruptions, where thick layers of lapilli can be deposited during a basal surge eruption.  Most lapilli tuffs which remain in ancient terrains are formed by the accumulation and ''welding'' of semi-molten lapilli into what is known as a [[Tuff#Welded tuff|welded tuff]].

The heat of the newly deposited volcanic pile tends to cause the semi-molten material to flatten out and then become welded. Welded tuff [[rock microstructure|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]].

===Accretionary lapilli===
[[File:Accretionary Lapilli - geograph.org.uk - 831917.jpg|thumb|Accretionary lapilli in the [[Mesoproterozoic]] [[Stac Fada Member]] of the [[Torridonian]], of probable impact origin]]
Rounded balls of [[tephra]] are called ''accretionary lapilli'' if they consist of layered [[volcanic ash]] particles.  Accretionary lapilli are formed by a process of wet [[Volcanic ash aggregation|ash aggregation]] due to moisture in volcanic clouds that sticks the particles together, with the volcanic ash nucleating on some object and then accreting to it in layers before the accretionary lapillus falls from the cloud.  Accretionary lapilli are like volcanic hailstones that form by the addition of concentric layers of moist ash around a central nucleus.

This texture can be confused with [[spherulite|spherulitic]] and [[axiolitic]] texture.

====Armoured (or cored) lapilli====
These lapilli are a variety of accretionary lapilli, though they contain lithic or crystal cores coated by rinds of coarse to fine ash.  Armoured lapilli only form in hydroclastic eruptions, where significant moisture is present.  The vapour column contains cohesive ash which sticks to particles within it.