{{Short description|Natural rock fragment larger than 10 inches}} {{About|large rocks|the city in Colorado|Boulder, Colorado|other uses}} [[Image:Balanced Rock.jpg|thumb|This balancing boulder, "Balanced Rock", stands in Garden of the Gods park in Colorado Springs, Colorado, United States.]] [[File:Boulder along the chief hike in Stawamus Chief Provincial Park, BC (DSCF7553).jpg|thumb|Boulder in British Columbia, Canada]] [[File:Kämmenkivi stone in Pisa, Kuopio, Finland.jpg|thumb|''Kämmenkivi'' stone on the Pisa hill in Kuopio, Finland]] [[File:Bolders on Mahendra Hills, India.jpg|thumb|Balanced granite boulders at Hyderabad, India]] In geology, a '''boulder''' is a rock fragment with size greater than {{Convert|25.6|cm|in|1|abbr=on}} in diameter.<ref name="Glossary2005">{{cite book | title=Glossary of Geology | publisher=American Geological Institute | editor-last1=Neuendorf | editor-first1=K.K.E. | editor-last2=Mehl | editor-first2=J.P. Jr. | editor-last3=Jackson | editor-first3=J.A. | year=2005 | location=Alexandria, Virginia | page=79 | isbn=978-0922152896| edition=5th }}</ref> Smaller pieces are called cobbles and pebbles. While a boulder may be small enough to move or roll manually, others are extremely massive.<ref name="Boulder">{{cite dictionary|title=Boulder|url=http://dictionary.reference.com/browse/boulder|dictionary=Dictionary.com|access-date=30 November 2025}}</ref> In common usage, a boulder is too large for a person to move. Smaller boulders are usually just called rocks or stones.
== Etymology == The word ''boulder'' derives from ''boulder stone'', from Middle English ''bulderston'' or Swedish ''bullersten''.<ref>[http://dictionary.reference.com/browse/boulder boulder. (n.d.)] Online Etymology Dictionary. Retrieved December 9, 2011, from Dictionary.com website.</ref> It was previously sometimes spelled '''bowlder''', which survives as a less common variant spelling.<ref>{{cite Merriam-Webster|bowlder}}</ref><ref>{{cite web |title=Bowlder |url=https://www.collinsdictionary.com/dictionary/english/bowlder |publisher=Collins English Dictionary |access-date=30 November 2025}}</ref>
== About == In places covered by ice sheets during ice ages, such as Scandinavia, northern North America, and Siberia, glacial erratics are common. Erratics are boulders picked up by ice sheets during their advance, and deposited when they melt.<ref name="Boulder" /> These boulders are called "erratic" because they typically are of a different rock type than the bedrock on which they are deposited. One such boulder is used as the pedestal of the Bronze Horseman in Saint Petersburg, Russia.
Some noted rock formations involve giant boulders exposed by erosion, such as the Devil's Marbles in Australia's Northern Territory, the Horeke basalts in New Zealand, where an entire valley contains only boulders, and The Baths on the island of Virgin Gorda in the British Virgin Islands.
Boulder-sized clasts are found in some sedimentary rocks, such as coarse conglomerate and boulder clay.
==See also== * Bouldering, free climbing performed on small rock formations or artificial climbing walls * Moeraki Boulders, unusually large spherical boulders found in New Zealand * Monolith, a geological feature consisting of a single massive rock * List of individual rocks * Floaters
==References== {{Reflist}}
==External links== {{Commons category-inline|Boulders}}
{{Coastal geography}} {{Authority control}}
Category:Rocks Category:Rock formations Category:Garden features Category:Natural materials