A boulder is a loose (uncemented) clastic rock consisting of boulders — large (10 [1] -20 cm in diameter and more) of rounded hard rock fragments, between which a smaller clastic aggregate may be present.
Boulders are classified in many ways. The size of the boulders are:
- small (diameter of boulders 0.2-0.5 m);
- medium (0.5-1 m);
- large (1-5 m);
- rough (more than 5 m). The upper limit, after which pieces of rocks cease to be boulders in a boulder is not precisely defined, but usually passes between 1 [1] and 10 meters.
According to the method of formation, boulders are divided into:
- alluvial ;
- proluvial ;
- glacial ;
- eolovo - eluvial ;
- coastal and marine;
- ground and underwater colluvial .
The most common multicomponent (“polymictic”) non-exfoliating boulders with a layer thickness from a fraction of a meter to several meters.
In the fragments, there are a variety of igneous , sedimentary and metamorphic rocks. For example, on the coasts of the Kola Peninsula, boulders in boulders are formed from metamorphic rocks, including gneisses , crystalline schists , amphibolites , quartzites , and in areas of modern and recent volcanism - from lavas and tuffs .
Notes
- ↑ 1 2 Boulderwood // Geological dictionary: in 2 volumes. - M .: Nedra. Edited by K. N. Paffenholz and others. 1978.
Literature
- Valunnik / V. T. Frolov // Greater Caucasus - Grand Canal. - M .: The Great Russian Encyclopedia, 2006. - P. 549. - (The Great Russian Encyclopedia : [in 35 t.] / Ed. Yu. S. Osipov ; 2004–2017, t. 4). - ISBN 5-85270-333-8 .