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Updated: May 24, 2025
In Syenite quartz is rare or wanting, hornblende taking the place of mica, and the proportion of silica not exceeding 50 to 60 per cent. Granite often preserves a very uniform character throughout a wide range of territory, forming hills of a peculiar rounded form, usually clad with a scanty vegetation.
Distilled or rain water should be used, as the calcareous salts contained in ordinary water would produce insoluble salts of lime, which would render the solution turbid and opalescent; this solution contains silica and potash combined together in the proportion of 70 to 30.
There are many other volcanic mountains, and also great numbers of mud volcanoes, hot springs and geysers. It is for the latter that the island is best known to geologists. Their waters are at or near the boiling point and contain silica in abundance.
Such remnant masses, if large, are known as outliers. When In the foreground are seen fragments of petrified trunks of trees, composed of silica and extremely resistant to the weather. Retreating cliffs may fall back a number of miles behind their outliers before the latter are finally consumed. Monuments are smaller masses and may be but partially detached from the cliff face.
I had expected to see a calcareous fountain, but found the most magnificent masses of silica of infinite variety of form; shallow cones with cylindrical summits, pyramidal flights of steps, round basins with ribbed margins, and ponds of boiling water.
He says: "While, however, there are not apparent signs of mechanical disturbances, during the long period that elapsed from the cooling of the earth's surface to the deposition of the Silurian and Cambrian systems, it is to be presumed that the internal igneous activity of the earth's crust was in full force, so that on the inner side of it, in obedience to the laws of specific gravity, chemical attraction, and centrifugal force, a great segregation of silica in a molten state took place.
The result of these two waters meeting would be that carbonate of lime would be formed, hydro-sulphuric acid would be set free, and sulphide of gold would be deposited, as well as silica, which was formerly held in solution by the carbonic acid."
Hair contains at least ten distinct substances: sulphate of lime and magnesia, chlorides of sodium and potassium, phosphate of lime, peroxide of iron, silica, lactate of ammonia, oxide of manganese and margaim. Of these, sulphur is the most prominent, and it is upon this that certain metallic salts operate in changing the color of hair.
David Forbes informs me that silica can crystallise in the dry way, and he has found in quartz forming a constituent part of some trachytes, both from Guadeloupe and Iceland, glass cavities quite similar to those met with in genuine volcanic minerals. These "glass cavities," which with many other kindred phenomena have been carefully studied by Mr.
At the beginning these injections have been the same as the first massive intrusive rocks, either granite or greenstone; but as the rocks gradually cooled, the fissures reached greater and greater depths; and the lighter constituents having been drawn off and exhausted, only the heavier molten silica, mingled with metallic and aqueous vapours, has been left, and with these the last-formed and deepest fissures have been filled.
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