Lapilli
Pyroclastic fragments with individual diameters from 2 mm up to 64 mm.
Language and route: Latin plural of lapillus ← lapis. Latin plural of lapillus ← lapis
Literal gloss: little stones
The name and its history
Inherited Latin word; individual geological coiner unknown · Latin diminutive; modern IUGS size grade
- What does the word literally mean?
- The immediate route is Latin plural of lapillus ← lapis. In its naming context it meant ‘little stones’; deeper associations must be distinguished from the geological term's original purpose. Use singular lapillus, plural lapilli; the grade does not depend on how rounded the fragment looks.
- What did the original author mean?
- Latin lapillus described a pebble; volcanic writers adopted it for small ejected stones.
- Why was the name needed?
- Rocks thrown from volcanoes vary enormously in size, requiring standardized descriptive grades.
- What evidence supported the original concept?
- Eruption deposits sorted by grain size, grain morphology and mode of transport.
- How has geology changed the concept?
- Modern lapilli includes diverse pumice, scoria, lithic and glass fragments within a size range; the word is not a claim about mineral composition.
Further historical context
Latin lapillus described a pebble; volcanic writers adopted it for small ejected stones.
Rocks thrown from volcanoes vary enormously in size, requiring standardized descriptive grades.
Eruption deposits sorted by grain size, grain morphology and mode of transport.
Modern lapilli includes diverse pumice, scoria, lithic and glass fragments within a size range; the word is not a claim about mineral composition.
Editorial qualification
Use singular lapillus, plural lapilli; the grade does not depend on how rounded the fragment looks.
Related names
Tuff · Volcanic ash · Agglomerate · Tephra
Sources
- Berlin–Brandenburg Academy, Lewis & Short Latin lapillus — Latin diminutive lapis “stone”
- BGS, lapilli-tuff — Modern 2–64 mm particle-grade classification
- British Geological Survey, Rock Classification Scheme — Authority for modern rock categories and distinctions
- USGS, classification of volcanic tephra and terminology — Modern terminology and historical usage of tephra