noun, plural lapilli [luh-pil-ahy] .
a small stony particle ejected from a volcano.

1740–50; < Latin: little stone, pebble, diminutive of lapis stone Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
lapillus (ləˈpɪləs)
n , pl -li
a small piece of lava thrown from a volcano
[C18: Latin: little stone]

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
lapillus   (lə-pĭl'əs)  Pronunciation Key 
Plural lapilli (lə-pĭl'ī')
A small fragment of lava, between 2 and 64 mm in size, blown out from a volcano.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica


unconsolidated volcanic fragment with a diameter between 4 and 32 mm (0.16 and 1.26 inches) that was ejected during a volcanic explosion. Lapilli may consist of fresh magma, solid magma from a prior eruption, or basement rocks through which the eruption passed. Accretionary lapilli are pellets formed by the accretion of volcanic ash or dust around moisture droplets; as in hailstones formed of water, these volcanic "hailstones" may show concentric rings-some as much as 10 cm (four inches) across-when they are carried through the eruption cloud several times by turbulent updrafts.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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