Weathering gravel

Close-up of granite gravel in the immediate vicinity of its parent rock (pocket knife for size comparison)

As Verwitterungsgrus , Gesteinsgrus or shortly crus ( low German ) is a mixture of different, square-edged, irregularly shaped mineral grains obtained by the weathering-related massive disintegration of rocks with granular structure is produced. The grain size of Grus ranges from 2 to 6 mm (corresponds to fine gravel). The disintegration process is known as abgrusung or gravel formation .

Aging mostly affects granites and chemically similar plutonic and metamorphic rocks. H. Granodiorite , diorite and gneiss derived from them . The cause is often temperature weathering : in the event of strong temperature fluctuations, the various minerals do not expand or contract to the same extent due to different thermal expansion coefficients , so that the interlocking of the grains in the rock structure gradually loosens. However, gravel formation can also take place through hydrolysis of the feldspars and mica. The structure is particularly weakened by the transformation of the feldspars into significantly softer clay minerals .

Grilling is a process that is often associated with wool sack weathering .

literature

• Hans Murawski, Wilhelm Meyer: Geological dictionary. 10th, revised and expanded edition, Enke , Stuttgart / dtv 3038, Munich 1998, ISBN 3-432-84100-0 (Enke) / 3-423-03038-0 (dtv). Current (the 12th) edition: Spectrum , Heidelberg 2010, ISBN 978-3-8274-1810-4 .

Individual evidence

1. ^ DIERCKE Dictionary General Geography, p. 296 May 1997