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IV.―On some Artificial Forms of Silica, illustrative of the structure of Agates, Chalcedonies, &c

Published online by Cambridge University Press:  14 March 2018

Extract

It is a common chemical fact, that when a solution containing an alkaline silicate is acted upon by any reagent capable of separating the silica from the base, the silica is in the majority of cases thrown down in a solid form. The fact of this reaction is all that, as a rule, the chemist would look at: but in addition to the mere chemical fact of the precipitation of the silica, another most important element from the mineralogist's point of view is that of the form in which this precipitate of solid matter appears. This form naturally varies with the various conditions of the experiment, and it is by the study of these varying forms that the authors have sought to elucidate, experimentally , the wondrous and beautiful varieties of structure which are so familiar to us in the endless forms of silica occurring in nature.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1882

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References

* Plate I, Fig. I. shews a group of such stalactitic growths of silica. At A and B these have come in contact with the aides of the containing vessel, and have thus been made, as it were, in section, shewing their hollow nature.

* Plate II shews two examples of this. In both preparations the growth has commenced by stalactitic forms comiug in contact with the sides of the containing vessel, and by continuing the action these have developed a series d successive bands external to the original tubes. The space beyond these bands consists of almost structureless silics due to the ultimate satm~tion of the alkaline silicate with the acid rengent.

Plate III, fig. 1.