Weathering stability
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The weathering stability (also weathering resistance , weathering resistance ) is an expression for how resistant a mineral or rock is to physically-mechanically, chemically, biologically and biochemically effective forces of weathering . Since there are sometimes considerable differences in the stability of a mineral towards different types of weathering, a statement about the general stability of a mineral towards all types of weathering and the associated variety of environmental conditions can only be made to a very limited extent. The most important factors that determine the weathering stability of a mineral are the type of ions and the bonds within the mineral crystal lattice , with layer and framework structures generally being the most stable. Particularly easily soluble minerals such as halite show a low stability under humid conditions, but this hardly plays a role under arid conditions. With a comparable grain size, the following stability series results: gypsum <calcite <dolomite << olivine <anorthite <apatite <augite <hornblende <albite <biotite <muscovite <orthoclase << quartz <magnetite <zirconium.
When speaking of the weathering stability of a rock, it must be taken into account that it usually consists of several minerals with different weathering stabilities, which in turn weather to different degrees. Rocks therefore show a weathering sequence within their mineral components, which leads to more stable minerals remaining as residues and thus changing the composition of the rock. Furthermore, the stability of rocks depends on: the type of rock, the structure, the fissures, stratification, foliation and the type of binding agent. The more compact the rock, the more stable it is. Coarse crystalline rock is more unstable than fine crystalline rock. The more pronounced the foliation, the more unstable the rock. Carbonatic binders are more likely to weather than clayey or oxidic ones.
literature
- Weather resistance. In: Lexicon of Geosciences. Volume V, Spektrum Akademischer Verlag, Heidelberg / Berlin 2002, ISBN 3-8274-0424-X .
- Winfried EH Blum: Soil science in brief. (= Hirt's headwords ). 7th edition. Gebr. Borntraeger, Stuttgart 2012, ISBN 978-3-443-03120-6 .