Amorphous mineral

A clay deposit usually contains nonclaylike minerals as impurities and these impurities may actually be essential in determining the unique and specially desired properties of the clay. Both crystalline and amorphous minerals and compounds may be present in a clay deposit (8). 

ACP reveals discoidal and spherical forms87, but it is questionable whether these two forms actually exist in living bone. It has been assumed to be more likely that they are produced by drying or aging of the sample materials. Amorphous mineral material occurs in matrix vesicles of newly synthesizing bone. This less dense amorphous mineral material appears to occupy the position of the vesicle membrane and it may be the precursor of bone material88. ... 

Birrell, K.S. and Gradwcll, M., 1956. Ion-exchange phenomena in some soils containing amorphous mineral constituents. / Soil. Sci, 7 130-147. 

The hydrated amorphous mineral silica (opal) is widely used by many plants and animals for structural purposes. Most skeletons are formed by unicellular organisms (diatoms Figure 2(a), radiolarians Figure 2(b)), but silica is also present within multicellular organisms (sponge spicules, plant... 

PROP Average density of 0.13. Expands when finely ground and heated. Natural glass, amorphous mineral consisting of fused sodium potassium aluminum silicate, containing <1% quartz. 

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). 

However, the reverse situation — that is, replacement of apatitic substance by quartz — has been described (Horowitz, 1967) as a dij enetic process in sediments, so it becomes difficult to understand the conditions of Eh and pH which govern reactions of this sort without a knowledge of the entire history of events although Cook (1970, p. 2115) has concluded that phosphatiza-tion and calcitization of silica, and the reverse reaction, may be explained by pH fluctuation, probably within the range of pH 7 to 10 . Furthermore, laboratory study of the system CaO-PaOs-HjO (Skinner, 1973) indicates that equilibrium obtains slowly even at temperatures about 300°C. While most minerals can be assumed to have formed under equilibrium conditions — in environments that existed at the time — it must be remembered that amorphous mineral substances [such as, bolivarite and evansite] have not attained a status of minimum energy during thousands to millions of years. 

Nanoparticles and the Environmenf targets naturally occurring, finely particulate minerals, many of which form at low temperature. Thus, many of the compounds of interest are those of the clay fraction . Of course, there have been decades of critical work on the structures, microstructures, and reactivity of finely crystalline or amorphous minerals, especially oxides, oxyhydroxides, hydroxides, and clays. We will not summarize what is known in general about these (for this, the reader is referred to earlier Reviews in Mineralogy volumes). Rather, our goal is to focus on the features of these materials that stem directly or indirectly from their size. 

The salt used to furnish the index cation should be relatively soluble in the alcohol used for sample washing. The low solubility of NaCl in ethanol has been a frequently overlooked source of error. The salt then dissolves during the subsequent extraction step and yields an anomalously high CEC value. Soils containing large quantities of hydroxyoxide or amorphous minerals may also retain salts in particle micropores, so that washing does not completely remove the salts. This also yields high CEC values. 

Micro-P. [DJ. Enterprises] Amorphous mineral silicate lightweight, stable, inert filler, resin extender for aitoaft, military, appliances, business machines, construction, consumer goods, elec electronic, land transport, and marine applies. 

I shall not discuss in further detail general applications of Mossbauer spectroscopy in geochemistry since relevant books, review articles, and original papers are available (1,7,8 9,10). The following sections are devoted to a few selected topics in this field, that is, Mossbauer studies of amorphous minerals and environmental samples. 

Amorphous Minerals. Mossbauer spectroscopy is useful for studying the structure and bonding of amorphous materials, because it is only sensitive to the configuration of the nearest neighbors and the oxidation states of the probe atoms in those systems (11)-... 

While a number of works have contributed to Mossbauer spectra of synthetic glasses (12-17), only a few studies have been reported on obsidians, which constitute a typical amorphous mineral of terrestrial origin. Although the Fe VFe ratios (0.32-0.45) in obsidians from... 

The second hypothesis is that the weathering of finely divided amorphous minerals is more intense in the zone under root influence than in the bulk soil. These minerals would be subjected to an aggressive environment characterized by a greater organic acids content and lower pH values (Seguin et al., 2004). The XRD results are in phase with this hypothesis as they indicate a depletion of most... 

Eraction 6. Amorphous mineral colloid-bound 0.2 M (NH4)2C204 (pH 3) (soil/reagent = 1 10) shake for 4 h (in the dark). 

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