Weathering process

There are approximately 3000 different minerals found in rock formations however, much of the Earth s crust consists of only 50 dominant mineral forms (Degens, 1989). The primary and secondary minerals commonly found in soils are listed in table 6.1. As mentioned above, chemical weathering processes in soils are important in the transformation of primary to secondary minerals. For example, when examining the weathering of feldspars (this most abundant group of minerals in the Earth s crust), K-feldspar is transformed into kaolinite through the following reaction  

During the formation of kaolinite, a K+ ion is also released from the soil, while A1 is retained in the solid phase. Similarly, the weathering of goethite by H+ can release Fe3+in the following reaction  

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In contrast to the sulfide ores, the lateritic ores were formed over long periods of time as a result of weathering of exposed nickel-containing rocks. The lateritic weathering process resulted in nickel solutions that were redeposited elsewhere in the form of oxides or siUcates. One type of laterite is nickeliferous limonitic iron laterite (Ee, Ni)O(OH) which consists primarily of hydrated iron oxide in which the nickel is dispersed in soHd solution. 

Chlorine plays a less significant role in chemical weathering processes than do sulfur and carbon. Most geochemists beHeve that much, or most, of the chloride in stream water in coastal areas is derived from sea salt that is carried landward or deposited by rainfall. Farther inland, however, a major part of the chloride loads in streams is the result of human activities. 

The atmosphere is nearly always in motion. The scales and magnitude of these motions extend over a wide range. Although vertical motions certainly occur in the atmosphere and are important to both weather processes and the movement of pollutants, it is convenient to consider wind as only the horizontal component of velocity. 

The surface rock formations of the earth are continually exposed to the weathering process of the atmosphere that surrounds the earth. The weathering process through... 

Weathered rock is bedrock that is deteriorating due to the weathering process. Usually this is confined to the upper layers of the bedrock. 

The weathering process which eventually reduces the rock of the parent material to the inorganic constituents of soil comprises both physical and chemical changes. Size reduction from rocks to the colloidal state depends not only upon the mechanical action of natural forces but also on chemical solubilisation of certain minerals, action of plant roots, and the effects of organic substances formed by biological activity. 

Weathering processes take an active part in the cycling of oxygen and carbon, but does chemical weathering affect these cycles to a significant extent Consider the following examples. 

Note that this estimate of the annual O2 loss to weathering processes is approximately equal to the estimated annual production of oxygen estimated above. Hence, the weathering of rocks and burial of organic carbon in sediments during their formation are important processes for the oxygen content of the atmosphere. 

Campbell, I. B. and Claridge, G. G. C. (1987). "Antarctica Soils, Weathering Processes and Environment." Developments m Soil Science, Vol 16. Elsevier, Amsterdam, The Netherlands. 

Stallard, R. F., Koehnken, L., and Johnsson, M. J. (1991). Weathering processes and the composition of inorganic material transported through the Orinoco River system, Venezuela and Colombia. Geoderma 51,133-165. 

The spectra of the rocks in the plains are very similar to the spectra obtained on the soil (see above). The ubiquitous presence of olivine in soil suggests that physical rather than chemical weathering processes currently dominate at Gusev crater. 

Meteorites on Mars. Meridiani Planum is the first Iron meteorite discovered on the surface of another planet, at the landing site of the Mars Exploration rover Opportunity [359]. Its maximum dimension is 30 cm (Fig. 8.38). Meteorites on the surface of solar system bodies can provide natural experiments for monitoring weathering processes. On Mars, aqueous alteration processes and physical alteration by Aeolian abrasion, for example, may have shaped the surface of the meteorite, which therefore has been investigated intensively by the MER instruments. Observations at mid-infrared wavelengths with the Mini-TES... 

The above considerations allow to understand the theoretically high potential of radioactive disequilibria in river waters for quantifying weathering processes at a watershed scale. 

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