Lapilli n. pl. : Volcanic ashes, consisting of small, angular, stony fragments or particles.

Example:
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Taxonomy
lapilli, accretionary, diameter, tuffs, particles, free encyclopedia, volcanic, ash, lapillus, volcanic ash, volcanic rock, texture, volcanic eruption, eruption, rocks, cloud, moisture, Armoured.

Defination from the web:
Lapilli on Fuerteventura ... Lapilli tuffs are a very common form of volcanic rock typical of rhyolite, andesite and dacite pyroclastic eruptions. Here, large thicknesses of lapilli can be deposited during a basal surge eruption. ...