Weathering grain surfaces

Courchesne F, Turmel MC, Beauchemin P. Magnesium and potassium release by weathering Spodosols grain surface coating effects. J. Soil Sci. Soc. Am. 1996 60 1188-1196. 

The thermodynamic incompatibility of many of the solid phases present with each other as well as their local environment, results in formation of secondary minerals. Although the secondary materials may comprise only a small volume fraction of the waste, they (1) tend to increase in amount with time, as weathering processes proceed, (2) typically form at grain surfaces and are thus physically liable to react with percolating gas or liquids, and (3) may exhibit sites suitable for sorption or crystallo-chemical incorporation of trace elements (see Donahoe, 2004). Frequently observed secondary minerals include jarosite and ettringite the former is known to sorb ions such as Mn and As, whereas ettringite can form solid solutions, in which SO4 is replaced by Cr04 (Kumarathasan et al. 1990). 

Meteorite regolith breccias (Fig. 11.6) are mixtures of fine-grained surface materials and coarser subsurface grains. Although they are perceptibly darkened, they do not show the spectral reddening that is characteristic of space weathering. 

Normally weathered (subaerial, surface alteration) basalts can contain nontronite (a ferric smectite) and celadonite which form at the same time but by pseudomorphism of different basalt mineral grains during intermediate stages of alteration (i.e., between rock and soil) as summarized by Righi and Meunier (1995). These observations would lead one to beheve that celadonite can be formed in terrestrial environments. If so, celadonite is not entirely restricted to relatively low-temperature hydrothermal formations in marine environments. It does not, apparently, form a significant mixed layer mineral series with smectite minerals as do glauconite and ilhte. 

Sand, the larger particles in soil, is composed primarily of weathered grains of quartz, which is a covalent solid of silicon dioxide. This constituent will have a relatively small surface area because of the large particle size and would not provide any significant binding sites for organic compounds. 

Groundwater environments can be represented as a simple flow-through system. For the situation where chemical weathering of mineral grains is transport controlled, the weathering rate of a mineral should be directly dependent on the rate of throughput of water. For the situation where rates are controlled by surface... 

The question of the influence of the road surface on tire wear cannot be answered unequivocally because of the large number of different compositions, state of use, and weather influences on their abrasive power. Road surfaces are also not durable enough for laboratory use. Hence, reliance has to be placed on the correlation between laboratory results on a laboratory abrasive surface and road test experience. Alumina of different grain size (but primarily 60) has proved to be the most useful. Even its sharpness changes with time of use and disks are limited in their useful life. 

Unprotected feedstock (e.g., hay or grain) should be destroyed. Although leaves of forage vegetation could still retain sufficient urticants to produce effects for a limited time, urticants are relatively nonpersistent on surfaces and should rapidly decompose depending on the level of contamination and the weather conditions. 

The weathering rate in d) corresponds to a "smoothed" line reflecting the actual data. The change with altitude is primarily caused probably by an increase in effective surface area of weathered mineral grains. With decreasing elevation more soil is produced partially also due to increased biological activity. 

Based on predicted weathering and erosion rates of the region, we estimate the profile to be several million years old. Because the soil has developed in situ, the topmost grains have reacted with water for the greatest extent of time. With depth, the total "lifetime" of the particles as soil decreases. This implies that the topmost quartz surfaces should be "reactively mature" (all fines removed, deep grown-together etch pits) and the bottom-most quartz surfaces should be "reactively young" (plentiful fines, fresh surfaces). ... 

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