Lapillus (plural lapilli)
is the 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¡Xsome as much as 10
cm (four inches) across¡Xwhen they are carried through the eruption cloud
several times by turbulent updrafts.
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