Obsidian rhyolitic

If elemental concentration rather than oxide concentrations are required, then the oxide conversion can be removed at this point. For obsidian (rhyolitic volcanic glass), using silicon as an internal standard yields results in very close agreement with the Gratuze approach, as shown in Table 37.1. 

The Coso Volcanic Field (CVF) in California, USA (Fig. 1) contains at least 38 high-silica rhyolite domes (Duffield Bacon 1981), many of which contain obsidian glass that has been quarried for tools by the indigenous population for more than 12,000 years. CVF obsidian... 

Figure 3.2 A zone of obsidian in a rhyolite flow-dome structure. (Redrawn with permission from Hughes and Smith, 1993 Figure 2A.)...

Diese Verfluchtigungsfolge wurde durch experimentelle Schmelz ver-suche von Lovering an Sand, Obsidian und Rhyolit bestatigt. 

Melts-Glass H20(v)-silicate glass Dobson et al. (1989) Ex +35 to+51 530-850 Natural rhyolitic obsidian and synthetic albite-orthoclase... 

Finally, Winther et al. (1998) studied diffusion of sulfur in dry albitic melt at 1300-1500°C and 1 GPa. They found that in this highly polymerized melt, sulfate ions are unusually stable, even at low fo. However, these are relatively immobile, and rapid speciation reaction takes place in this case, to form some S2 and S3 ions. The sulfate ions are still less mobile than sulfides but are nevertheless the dominant sulfur transport species in albite melt. The resulting transport rates, given by Dsui r = 1.47 x 10 (cm /sec) exp(-458,100/RT) are significantly slower than the other rates reported above, where diffusion is presumably controlled by motion of sulfides. As expected, these diffusivities are closest to the rates for dry rhyolite and obsidian obtained by Baker and Rutherford... 

Table III. Chemical Compositions of Fresh and Altered Rhyolitic Obsidian, and the Gain and Loss of Chemical Components During Zeolitic—Argillaceous Alteration0...

Perlite (rhyolitic obsidian) Aggregate in plasters, loose-fill insulation, filtration medium, paint filler, oil-well drilling muds, inert packing materials. 

Obsidian Dark amorphous igneous rocks with a rhyolitic chemical composition, conchoidal fracture and brittle, sometimes devitrification figures. 

Monitoring the amount of material removed by the laser and transported to the ICP is conqjlicated making normalization of data difficult Conditions such as the texture of the sanq>le, location of the sample in the laser cell, surface topography, laser energy, and other hictors affect e amount of material diat is introduced to the ICP torch and thus the intensity of die signal monitored for the various atomic masses of interest In addition, instrumental drift affects count rates. With liquid sanqiles internal standards typically are used to counteract instrument drift, but this approach is not feasible when material for the analysis is ablated from an intact solid sanqile. If one or more elements can be determined by another analytic technique, dien these can serve as internal standards. In the case of rhyolitic obsidian, which has relatively consistent silicon concentrations (ca. 36%), we have determined that silicon count rates can be normalized to a common value. Likewise, standards are normalized to their known silicon concentrations. This value, divided by the actual number of counts produces a normalization factor ftom i ch all the odier elements in that san le can be multiplied. A regression of blank-subtracted normalized counts to known elemental concentrations in the standards yields a calibration equation that can be used to calculate elemental concentrations in the samples analyzed. 

On the other hand, volcanic material may cool down so slowly that all of the gases do have time to escape. The result is the formation of rocks like basalt that are very hard and dense compared to pumice. Of course, there are several rocky materials that can form in-between these two extremes and that can have varying mineral compositions and grain sizes, resulting in various other igneous rocks such as granite, diorite, gabbro, rhyolite, and obsidian. 

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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