Mineral surface crusts

The geological process of the formation of serpentine from peridotite probably involves the synthesis of carbon compounds under FTT conditions (see Sect. 7.2.3). The hydrogen set free in the serpentinisation process can react with CO2 or CO in various ways. The process must be quite complex, as CO2 and CO flow through the system of clefts and chasms in the oceanic crust and must thus pass by various mineral surfaces, at which catalytic processes as well as adsorption and desorption could occur. 

Equations such as equation (1) above imply that the oxidative dissolution of pyrite is congruent, directly liberating Fe2+, SO4, and H+ to solution. However, in the common circumstance that water is insufficiently abundant to immediately transport the oxidation products away from the mineral surfaces, pyrite oxidation more commonly results initially in the accumulation of various hydroxysulphate evaporite minerals. These minerals form efflorescent crusts, typically white and yellow in colour, on the surfaces of pyrite-rich coals and mudstones (Fig. 1), and they effectively store the oxidation products in a readily soluble form until some hydro-logical event delivers sufficient water to dissolve and transport them away. Because pyrite often occurs in mudstones, where Al-bearing clay minerals are in contact with acidic pyrite oxidation waters, A1 is frequently released from the clays and is also stored in these hydroxysulphate phases. When these minerals finally dissolve, they result in abrupt and extreme increases in dissolved acidity. For this reason, they have been termed acid generating salts (AGS) (Bayless... 

Weathering reactions are caused by the interaction of water and air with the near surface of compounds contained in the crust of the Earth. Such reactions are slow, and the rates are sensitive to water flow and/or to the rate of mineral surface reactions. Surface runoff interacts minimally, but infiltrating and percolating water has an intense interaction. 

The most important class of interfacial reactions affecting the environment involves aqueous solutions reacting with mineral surfaces in the earth s outer crust (Stumm et al. 

Potassium (K) is much more reactive than sodium it ignites quickly on exposure to humid air and, therefore, should be handled under the surface of a hydrocarbon solvent such as mineral oil or toluene (see Sodium). Potassium can form explosive peroxides on contact with air. If this happens, the act of cutting a surface crust off the metal can... 

Watchman et oL (2000) Watchman, A.L. David, B. McNiven, I.J. Flood, J.M. Micro-archaeology of engraved and painted rock surface crusts at Yiwarlarlay (the lightning Brothers site). Northern Territory, Australia Journal of Archaeological Science 27 (2000) 315 325 Watchman et al. (2001) Watchman, A. Ward, 1. Jones, R. O Connor, S. Spatial and compositional variations within finely laminated mineral crusts at Carpenter s Gap, an archaeological site in tropical Australia Geoarchaeology - An International Journal 16 7 (2001) 803-824... 

Completely dense or dry rocks occur infrequently in the near surface crust. These rocks have—except for ores or graphite-containing rocks— very high resistivities (mostly >10 nm). The dielectric permittivity is usually relatively low and in the range of the dominant rock-forming minerals (3-5) accessory minerals (for example ores and graphite) can produce higher values. 

Six elements are metalloids B, Si, Ge, As, Sb, and Te. Of these, silicon is by far the most abundant, making up over 27% of the Earth s crust, more than any other element except oxygen, hi fact, S1O2 and silicate minerals account for 80% of the atoms near the Earth s surface. Despite its great abundance, silicon was not discovered until 1824, probably because the strong bonds it forms with oxygen makes silicon difficult to isolate. Two much rarer metalloids, antimony (known to the ancients) and arsenic (discovered ca. 1250 ad) were isolated and identified long before silicon. 

The corrosion of metals and alloys generally starts at the surface with the formation of an outer layer, which may develop into a crust of corrosion products. If a crust is formed, it generally has a layered structure comprising two or more compounds (1) an outer, rather stable, mineralized layer that often covers entirely the surface of the objects, and underneath, (2) a less mineralized, unstable, and chemically active layer. Some corrosion layers may also bind ugly and disfiguring earthy accretions. 

The melting process and the differentiation of the Earth s matter according to its density caused the lighter crust minerals to migrate to the outer layers of the still young Earth, whose surface temperature at that time was such that it was covered by a sea of melted rock (Wills and Bada, 2000). This separation of materials led to the layer structure of the Earth ... 

White and yellow evaporite minerals form thin crusts on the surface of and within fissures in the tailings. XRD analyses identified the hydrated iron sulphates, melanterite (FeS04-7H20), Zn-melanterite ((Zn,Fe)S04-7H20),... 

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