Colloids and Intrusions

Many granite complexes are permeated by fractures, which are filled with a white, quartz-rich rock, the so-called aplite.  Here it is not a matter of material which has crystallized out of thermally-heated water, as is common in the fractures of limestone, but rather of rock material which has penetrated directly in a fluid form.  What is of interest are the unique forms which present themselves here.

The pictures in the right-hand column illustrate lighter-colored aplite veins in the crystalline rocks of the Bernina and Gremsel regions of Switzerland.  The darker rock sections are granodiorite an diorite, granite-related rocks.  The left-hand column again shows experiments with colloids, in which dark-colored gelatenous material (agar) is submerged in lighter-colored colloidal material, and then deformed by pressure from outside.  One of the left-hand pictures shows dried meat.

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These formations are normally explained as resulting from high-temperature, ductile magmatic processes.  One can ask, however, whether the bands, shards and block-like breakage forms and the penetration into thin fractures do not indicate conditions which lie closer to a silicious, water-rich mineral colloid.  Is it possible these ductile deformations did not occur at a magmatic temperature of a thousand or more degrees, but rather in a moderate temperature of several hundred degrees in a heavy, firmly-gelled silica material with a high content of water and silicic acid?

One can ask, in addition, whether some of the fractures are not due to shrinkage as a consequence of the expelling of chemically-bound water.  Shrinkage cracks in the carbonaceous material of wood, for example, originate when a portion of the carbon, along with oxygen, escapes as carbon dioxide.

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