Volcanic glass shards

Bentonite is a rock rich in montmorillonite that has usually resulted from the alteration of volcanic dust (ash) of the intermediate (latitic) siliceous types. In general, reUcts of partially unaltered feldspar, quartz, or volcanic glass shards offer evidence of the parent rock. Most adsorbent clays, bleaching clays, and many clay catalysts are smectites, although some are palygorskite [1337-76 ]. 

Perkins, W. T., Pearce, N. J. G., and Westgate, J. A. (1997). The development of laser ablation ICP-MS and calibration strategies examples from the analysis of trace elements in volcanic glass shards and sulfide minerals. Geostandards Newsletter 21 175-190. 

Macdougall D. (1971) Fission track dating of volcanic glass shards in marine sediments. Earth Planet. Sci. Lett. 10, 403-406. 

Another problem is the increased water absorption of the autoclaved aerated concrete elements, therefore water retarding additives, e.g., cellulose esters, are used in the mixture of plasters. Due to an insufficient amount of water in the mixture of plasters, the hydration of the cement minerals slows down. The influence of natural zeolite and clinoptilolite on the properties of plaster has been investigated (45). Clinoptilolite is a natural zeolite comprising a microporous arrangement of silica and alumina tetrahedra (46). It commonly occurs as a devitrification product of volcanic glass shards in tuff and as vesicle fillings in basalts, andesites and rhyolites. 

Pearce, N.J. G.,Westgate,J. A., and Perkins, W.T. (1996). Developments in the analysis of volcanic glass shards by laser ablation ICP-MS Quantitative and single internal standard-multi-element methods. Quaternary Ini., p. 213. 

Macdougall (1971) used fission-track dating of glass shards to determine the ages of volcanic layers in deep-sea sediments. He compared his results to K/Ar dates and showed that both methods gave identical results (Table 2). 

The chemical composition of shards of volcanic glass from the 906-m core drilled dnring 1977/78 at Dome C (Lorius et al. 1979 Thompson et al. 1981) places them at point 5 in the trachyte field of Fig. 17.44. These particles originated from a depth of 726 m in the Dome-C core and were deposited about 25,000 years ago. Therefore, these tephra could also have originated from Mt. Takahe in spite of the great distance between Dome C and Mt. Takahe. The dispersion of tephra from Mt. Takahe may have been facilitated because the summit of this volcano is within 3,600 and 6,400 m of the boundary between the troposphere and the stratosphere. Therefore, the volcanic ash erupted by Mt. Takahe could have been injected directly into the stratosphere where it spread widely across Antarctica (Kyleetal. 1981). 

Selected crystals of sanidine and shards of volcanic glass were dated by the Ar/ Ar method at the Berkeley Geochronology Center. In addition, exposure ages were determined by means of in-situ produced cosmogenic radionuclides (Brown et al. 1991 Brook et al. 1993). The "Ar/ Ar dates derived from volcanic ash in Arena Valley and from sites in the western Asgard Range are listed in Appendix 19.9.1. 

Rhyolite is an example of even more siliceous (as much as 70% Si02), or acidic, volcanic material. Rhyolite is a product of rather extreme chemical fractionation relative to the average composition of Earth. It is a common material, but hardly abundant in comparison with basalt, or even andesite. Rhyolitic lavas mainly appear in regions where less extreme types of lavas predominate. Such silica- and alkali-rich materials as rhyolites melt at lower temperatures than basalts or andesites and produce viscous liquids. On cooling, many fail to crystallize, but produce obsidian glass. Some are so forcibly ejected that they erupt as shards of glass, producing widespread falls of volcanic ash and pumice. 

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