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accretionary lapilli

Volcanology
Small spherical balls of volcanic ash
Accretionary lapilli in an ash deposit on Santorini.

accretionary lapilli in an ash deposit on Santorini.
accretionary lapilli are small spherical balls of volcanic ash that form from a wet nucleus falling through a volcanic ash cloud. They can flatten on hitting the ground or may roll on loose ash and grow like a snowball.