In geology, a boulder is a rock fragment with size greater than 25.6
centimetres (10.1 in) in diameter. Smaller pieces are called
cobbles and pebbles. While a boulder may be small enough to move or
roll manually, others are extremely massive. In common usage, a
boulder is too large for a person to move. Smaller boulders are
usually just called rocks or stones. The word boulder is short for
boulder stone, from
Middle English bulderston or Swedish
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. They are called "erratic" because
they typically are of a different rock type than the bedrock on which
they are deposited. One of them 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
The Baths on the island of
Virgin Gorda in the British
Boulder sized clasts are found in some sedimentary rocks, such as
coarse conglomerate and boulder clay.
The climbing of large boulders is called bouldering.
^ Wentworth C.K. (1922). "A scale of grade and class terms for clastic
sediments". Journal of Geology. 30 (5): 377–392.
^ a b "Boulder". Dictionary.com. Retrieved 24 August 2013.
^ boulder. (n.d.) Online Etymology Dictionary. Retrieved December 9,
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