Volcanic ash partings

Because many geologists are not aware that volcanic ash partings occur in coals, it is difficult to interpret the absence of published reports regarding their occurrences. The abundance of such partings is probably much greater than presently recognized. 

The following generalities regarding their distribution are mainly limited to North America and are based primarily on our own observations, discussions with others, and interpretation of published reports. Specific references to recognized volcanic ash partings in coals are relatively few and restricted mostly to the past few years. 

For those interested in mineral matter in coal, an awareness that some partings may be of volcanic origin may be useful in explaining the distribution of some of these layers and the occurrences of some unusual components, such as strontium, phosphate, or uranium. Volcanic ash partings are likely to be more widespread and uniform in texture, composition and thickness than the more common partings of fluvial origin. They are also more likely to show marked differences from layer to layer, and to contain exotic mineral or chemical components. 

The lava flows in the Queen Alexandra Range and in the Marshall Mountains are interbedded in a few places with layers of tuff and lacustrine sediment. The lake sediment consists largely of finely laminated volcanic ash, partly replaced by calcite, and containing abundant organic debris including conchostracan, fish remains, and fragments of wood and plants. The composition of the volcanic ash and of the lacustrine sediment appears to be felsic, indicating that silicic ash was apparently erupted contemporaneously with the basalt lava flows. The presence of lacustrine sediment means that, at certain times, the volcanic eruptions ceased... 

Sediments of Tertiary and Quaternary age, including volcanic ash and aeolian materials, make up the parent material of the soils. In the more arid parts of the Andean System (the coastal plain of Peru and Chile, and the Altiplano of Bolivia) the topography is level. The Altiplano is a very large closed basin with numerous salt flats. In northwestern Argentina, the planar topography is broken by mountains composed of Precambrian rocks and Quaternary sediments. 

Part of the volcanism in the deep sea produces volcanic ash — small glassy splinters of basaltic matter, which widely occur in deep- sediments. This material (called pyroclastica) weathers relatively quickly because of its instable glassy structure and large surface. How far it contributes to the manganese supply of the deep sea, we cannot say yet, but Beiersdorf considers that it plays a dominant role in the creation of manganese nodule fields. 

Fig. 14. Different particles occurring in radiolarian ooze Black micronodules, patchy clay aggregates, glassy sharp dged fragment volcanic ash. (Clay aggregates can partly be formed as weathering products of volcanic ash or partly be new built).

The main secondary products are clay minerals, either smectite or kaolinite. These clay minerals are derived mainly and most readily from glass, but feldspars, amphiboles, pyroxenes, and biotite also alter in part to clay minerals. The alteration of volcanic ash to kaolinite involves removal of Ma, Ca, Mg, K and Fe as well as considerable silica. Pure kaolinite corresponds to a mixture of subequal amounts of silica and alumina plus a small amount of water and virtually nothing else—this is thus the product of very intensive leaching. Smectite on the other hand requires some Mg and more silica than kaolinite. It is thus the product of less intensive leaching than that which produces kaolinite. 

High temperature subsurface water leaches out ions and minerals from the rocks in its contact, and turns into a hot aqueous solution known as hydrothermal solution. It rises through cracks and fractures and picks up dissolved minerals and elements on its way, thus altering the original minerals of the rock to form new minerals. Generally the cations of the original minerals are partly leached out by the hydrothermal liquid, and water molecules enter their structures. Consequently cation-deficient hydrous minerals are formed, a sizeable portion of which are clay minerals. Examples include the formation of halloysite deposits by low temperature hydrothermal alteration of volcanic ash of Northland, New Zealand (Harvey and Murray, 1993) and formation of hectorite by hydrothermal alteration of Li -Mg rich basaltic ash (Harvey and Lagaly, 2006). 

Bavaria, Germany), Vicenza (Italy), Otavi (Namibia) and Okehampton (Devon, England). Montmorillonite together with beidellite form a significant part of bentonite (q.v.), a clay mixture derived from the weathering of volcanic ash montmorillonite is also a principal component of Fuller s earth (q.v.), a clay mixture with well-known absorbent properties (Deer et al., 1992). 

This paper is structured as follows in the first part, the characteristics of the natural phenomenon are described and a brief section has been devoted to the description of a typical wastewater treatment in the second part a methodology for the quantification of the critical thicknesses of volcanic ash accumulated on the screens is proposed finally the application to a case-study, which is the area surrounding Mt. Etna is shown. 

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