Ask the Chatbot Games & Quizzes History & Society Science & Tech Biographies Animals & Nature Geography & Travel Arts & Culture ProCon Money Videos
lapillus
Introduction References & Edit History Quick Facts & Related Topics
Images
lapillus A chart categorizes common textural terms for rocks by grain size in millimeters, dividing them into igneous and metamorphic, sedimentary, and pyroclastic types, with terms like phaneritic, sand, silt, breccia, and ash shown in relation to size.
Quick Facts
Plural:
Lapilli
Related Topics:
lapillistone
ejecta
See all related content
Britannica AI Icon
Adding us as a Preferred Source tells Google you trust our content, so our articles show up more often in your Google Search, Discover feed, and AI Overviews.
verifiedCite
While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions.
Select Citation Style
Feedback
Corrections? Updates? Omissions? Let us know if you have suggestions to improve this article (requires login).
Thank you for your feedback

Our editors will review what you’ve submitted and determine whether to revise the article.

External Websites
lapillus
lapillus Lapilli on Kilauea volcano, Hawaii.

lapillus

volcanic ejecta
Also known as: lapilli
Written and fact-checked by
Britannica Editors
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....
Britannica Editors
History

lapillus, 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.

This article was most recently revised and updated by Amy Tikkanen.