Noncrystalline minerals

Fig. 3. Soil inventory of carbon in soil organic matter (SOM) (a), A14C of SOM (b), noncrystalline minerals (c), and crystalline minerals (d) versus age of soil substrate. Filled circles, total profiles filled triangle, surface (O and A) horizons (Tom et al. 1997).

Another important consideration is the relative size of enzymes versus that of micropores (less than 2nm) in environmental particles which are especially abundant in noncrystalline mineral phases. Simple biomolecules (e.g., glucose, MW = 180 Da) can readily enter into micropores and can become stabilized by reacting with the mineral surface, whereas large macromolecules such as enzymes [e.g., laccase, MW = 60,000Da and diameter = 5nm (Andersen et al., 1996)] cannot enter and react with the trapped biomolecules. 

Figure 6.5. Changes in soil organic C storage and mineral content along a chronosequence in Hawaii (Torn et al., 1997). The substrate for soil development are basaltic ash deposits of known age. Climate and vegetation are virtually the same across the sites. (A) Soil organic C inventory versus ash substrate age. The solid line is the whole mineral soil to the C horizon, and the dashed line is the top 20 cm. The increase and subsequent decrease in SOM with soil age is mostly due to changes in the subsurface mineral soil. (B) The correlation of soil carbon in mineral horizons with the amount of noncrystalline minerals.

Figure 30 Content of (a) organic C, (b) A C, (c) noncrystalline minerals, and (d) crystalline minerals versus age along a chronosequence of soils on the Hawaiian Islands. Filled circles represent total soil profile and filled triangles represent surface (O and A) horizons only (Torn et al., 1997) (reproduced by permission of Nature Publishing Group from Nature, 1997, 389, 170-173).

Deposition involves the formation and precipitation of both crystalline and amorphous (noncrystalline) scales and the ultimate adherence of these mineral salt scales onto a heat transfer surface. Problems of deposition have the deleterious effect of reducing the rate of heat transfer, thus increasing the heat input requirements and raising the costs of operation. In addition, deposition reduces the efficiency of cooling the fabric of the boiler (especially the heat transfer metals), which leads to long-term problems of fatigue failure. 

Ceramic materials are typically noncrystalline inorganic oxides prepared by heat-treatment of a powder and have a network structure. They include many silicate minerals, such as quartz (silicon dioxide, which has the empirical formula SiO,), and high-temperature superconductors (Box 5.2). Ceramic materials have great strength and stability, because covalent bonds must be broken to cause any deformation in the crystal. As a result, ceramic materials under physical stress tend to shatter rather than bend. Section 14.22 contains further information on the properties of ceramic materials. 

XPD [18]. Similarly, mineral impurities in talc were analyzed by polarizing light microscopy, differential thermal analysis, and XPD [19]. It must be recognized, however, that small amounts of crystalline impurities (usually <0.5% w/w) may not be detected by XPD. In case of noncrystalline impurities, mrch higher concentrations may be nondetectable. 

This information is reported as the percentage that each of the clay mineral type contributes to total identifiable clay mineral content of the noncarbonate clay-sized fraction of the surface sediments. These percentages were determined by x-ray diffraction, which is luiable to identify noncrystalline solids. Using this technique, clay minerals were found to comprise about 60% of the mass of carbonate-free fine-grained fraction. Most of the noncrystalline soUds are probably mixed-layer clay minerals. Carbonate was removed to facilitate the x-ray diffraction characterization of the clay minerals. In some cases, roimd off errors cause the sum of the percentages of kaolinite, illite, montmorillonite, and chlorite to deviate slightly from 100%. 

Certain polysaccharides are normally hydrolyzed with mineral acid, usually sulfuric acid, either by direct refluxing with dilute acid or by preliminary dissolution in concentrated acid. Typical procedures have been described, and the associated problems discussed.22,23 Although prior solution of the polysaccharide in 72% sulfuric acid is a standard procedure,24 it has been shown that part of the carbohydrate may become sulfated, leading to erroneous results.23 When noncrystalline polysaccharides are being hydrolyzed, the treatment with 72% acid may be slightly modified.26 In special situations, oxidative hydrolysis, for example, of carrageenan, may be achieved by using sulfuric acid in the presence of bromine.27... 

Glasses and ceramics are inorganic materials that have been produced for thousands of years see Oxides Solid-state Chemistry and Noncrystalline Solids). Traditionally they are made from natural raw minerals such as clays or sand. Crystalline ceramics are shaped by adding water to clays in order to produce a plastic material and then heated in a furnace. Amorphous glasses are made from the melt and shaped by moulding near their softening temperatme. In both cases, high temperatmes are required. 

Carbonaceous material is widespread throughout CP IDPs both as discrete inclusions of noncrystalline material and as a semicontinuous matrix with embedded mineral grains. Often it has a vesiculated appearance consistent with an organic component (Figure 7(a)). The bulk abundance of carbon in CP IDPs varies from —4% to 45% with an average of 13% (Keller et al., 1994). In contrast to the fine-grained matrices of carbonaceous chondrites, ordered... 

Across a chronosequence of soils on the Hawaiian islands (Crews et al., 1995), Tom et al. (1997) found that both the quantity of stored carbon and its turnover time correlated with the noncrystalline (allophane, imogolite, and ferrihy-drite) mineral content of the soil (Figure 30). These amorphous minerals possess a unique geometry with a very high surface area (Table 13) which facilitates the formation of highly stable bonds with SOM (Oades, 1988). 

Crystalline silica includes the silica minerals quartz and its polymorphs such as cristobalite and tridymite, which have the same chemical formula but different crystal structures. Amorphous, noncrystalline silica can also occur in a wide variety of geologic environments (Ross, 1999). 

In Andisols, Oxisols, Ultisols, and the B horizons of Spodosols, HSs occur largely as complexes with Al and Fe or their respective poorly crystalline and noncrystalline oxides (Oades et al., 1989 Theng et al., 1989). In soils with little organic matter and in subsoils, mineral colloid—microbe interactions are governed largely by the mineralogical composition and pH of the system. 

Manganese oxides, which have different structural and surface properties, vary substantially in their ability to promote the precipitation and crystallization of Fe oxides and oxyhydroxides. The Mn(II) dissolved from Mn oxides in the presence of Fe(II) also influences the crystallization of oxidation products of Fe(II). The Fe oxides formed as influenced by Mn oxides and dissolved Mn(II) range from lepidocrocite, goethite, maghemite, dkaganeite, feroxyhyte, magnetite, honessite-like minerals, to noncrystalline Fe oxides. Therefore, Mn oxides deserve close attention in the genesis of Fe oxides. 

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