noun
lapilli
Geological term for small volcanic fragments (2–64 mm) ejected during an eruption.
火山礫は噴火の際に火口から放出される。
Lapilli are ejected from the crater during an eruption.
火山灰 is volcanic ash (<2 mm), finer than 火山礫.
Compound of 火山 (volcano) and 礫 (small stone, pebble).