Allophanes rocks

Solubility calculations were added for two allophanes, for which the equilibrium constants and formulae are a function of pH. Paces (74) found cold ground waters collected from springs in granitic rocks of the Bohemian Massif of Czechoslovakia to be supersaturated with respect to kaolinite while being unsaturated with respect to amorphous silica. He interpreted this as an indication that a metastable aluminosilicate more soluble than kaolinite was controlling the concentrations of alumina and silica in these waters. This aluminosilicate was further hypothesized to be of varied chemical composition, controlled by the mole... 

Compound Average of Igneous Rocks (%) Hydrous Mica (Scotland) (%) Montmoril- lonite (France) (%) Kaolinite (Virginia) (%) Allophane (Belgium) (%)... 

Phosphates are fixed by Fe-hydroxides and together with these by clay minerals. In tropical soils, phosphorus fixing on Fe-com-pounds is widespread. Phosphate fixation is appreciable in soils rich in allophane, derived from volcanic rocks. 

After 1950 the application of such methods by workers in Japan (Aomine and Yoshinaga [1955]) and New Zealand (Birrell and Fieldes [1952]) showed that certain ando soils from volcanic ash in Japan and in New Zealand all classes of both yellow-brown pumice soils derived from rhyolitic volcanic ash and yellow-brown loams derived from andesitic and from rhyolitic volcanic ash had clay fractions composed predominantly of allophane (Fieldes [1953, 1955]). The ability to obtain allophane relatively free from crystalline material and the high proportions in Japan and New Zealand of agriculturally important land derived from volcanic ash encouraged the study and elucidation of the properties of allophane in both countries at an early date. Subsequent work in other countries confirmed that allophane was a common constituent of volcanic ash soils. Allophane was also shown to be present in high proportions in clay fractions of weakly developed soils derived from basalt (Fieldes [1953]) or from other basic rocks (Mitchell and Farmer [1962]). In addition, in recent years serious attention has been given to the more difficult problem of assessing amounts of allophane in the presence of crystalline clay constituents in soils of many different kinds (Mitchell and Farmer [1962]). 

Modes of origin of allophane have been discussed by Fieldes [1962, 1966]. The latter paper suggests that structural randomness is the principal intrinsic property of allophane. Allophane is frequently produced by weathering of glasses and other disordered aluminosilicates or by processes leading to fast precipitation or very fine subdivision (Fieldes and Furkert [1966]) which are likely to result in random structures. Allophane accumulates in soils where soil conditions favor the persistence of random structures. Effects of this nature on the formation of allophane in rocks and soils are summarized briefly below. 

The occurrence of allophane in rocks is associated with conditions that favor formation of random-structure aluminosilicates. Thus, allophanes of geological origin that occur in fissures of ore veins, on linings of cavities in marl, and in similar locations, appear to have been formed by precipitation at relatively low temperatures and pressures from solutions containing silicon and aluminum. Hydrous aluminosilicates prepared artificially in a similar... 

Kanno [1964] described the occurrence of allophane in a humic allophane soil from the Tachikawa loam bed of a soil in Mitaka, Tokyo, derived from basaltic ash. Similarly, the amorphous clays from certain soils from basalt of northern Ireland and many other parts of the world are allophanic, and the amorphous clays in young soils derived from ultrabasic rocks such as dunite in New Zealand clearly have allophanic constituents, though these may be inseparable from gels of hydrous iron oxides, antigorites, and other secondary minerals. 

Table 4. Amounts of Allophane (Estimated by Dissolution) and Clays Other Than Allophane in Subsoils of a Range of Soils from Sedimentary Rocks...

Allophanes originating from rock grinding or from action of soil processes on sedimentary rocks are usually associated with clay minerals as well as other clay-size materials. Weathering sequences for such materials are liable to be complicated. However, sequences involving allophane derived from volcanic ash and basalt are more straightforward and these have been studied. Results of such studies are in some respects well established but other aspects remain open to discussion. 

Tokudume and Kanno [1967] show that the ratio of humic to fulvic acids in the organic matter of Japanese soils from volcanic ash is much higher than in the organic matter of Red-Yellow soils from sedimentary rocks. The humic acids of volcanic ash soils also are more aromatic. There is evidence that the alteration of fulvic acids to humic acids may be accelerated by the catalytic action of allophane (Kyuma and Kawaguchi [1964]). 

Allophane, imogolite Fieldes and Furkert [1966], Mitchell et al [1964], Wada [1967a]. Rock-forming Silicates Lyon [1962b], Moenke [1962a]. 

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