Colloids and Serpentinites

Examples of serpentine include types which are penetrated by a net of lighter veins.  They can also give rise to ideas involving an origin in a gel consistency.

The left-hand column of pictures shows forms created with gelled colloids:  through the shaking of a darker, half-solidified gel and the simultaneous penetration by an added white, more fluid gel, net-like fracture forms and flowing breakage structures are created.  In the right-hand column, for comparison, are pictures of serpentinite from Switzerland and Italy.  Serpentinite often shows a breccia structure.  The white veins consist of calcitic and dolomitic minerals.

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Although serpentinites can appear similar to marble, and commercially the two are often grouped together, they have little in common.  The present understanding of serpentinites is that they are metamorphosed sea-floor rocks, transformed at depth under great heat and pressure.

Serpentinite, Turkey                                                        Serpentinite, Italy

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Serpentinite with white matrix-zones, in which broken pieces of the darker rock swim:
 
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One has the distinct impression with these formations, that the calcite was not deposited afterwards within the growing fractures, but rather that it was present in a malleable or fluid form, mixed with the darker material, and thereby could also embed broken pieces of the latter within itself.  Here it can hardly be a matter of a classical magmatic melt, or a slow reforming in a solid condition under pressure, but rather a mixture of soft and fluid substances with correspondingly lower temperatures and higher water content.

The serpentinite, in a particular phase of the development, could have been in a colloidal condition similar to cheese, with a thinner matrix and having a larger percentage of bound and free water.  The presently-assumed volcanic-magmatic undersea processes would then have conceivably been in a lower temperature range of perhaps 400 - 800°  (a lowered melting point due to higher water content).  Such a picture would not contradict the occasionally-observed pillow formations of serpentinite.

There exists, from an unexpected source, an indication that such conceptions cannot be ruled out.  In eastern Turkey are found, in the neighborhood of serpentinite-formations, massive deposits of amorphous silica rocks (hornfels, jasper), which must have been in the form of a silicious gel at the time of their deposition.  The geologist Karl Nebert, who researched this phenomenon in the 1950's, concluded that after the decline of volcanic-magmatic agtivity in the region, great outpourings of highly-saturated silica solution took place.  This solution, emerging from fracture zones, would then have converted with cooling into a colloidal-gelatenous form and then been embedded into the serpentinite and the following sediments.  Only in this way could Nebert explain the size of the silica deposits as well as their alternating deposition, on the one had with serpentinite, and on the other with schists and limestone.  The presence of radiolarians (single-celled animals with silica skeletons) in isolated as well as massively-deposited form, complicates the picture.  Nebert explains them as the result of a favorable mileau which resulted from the presence of the volcanically-originating silica in the water of the region.

One could ask oneself, however, why such phenomena (gelatenous silica-spheres and lenses, as well as silica layers hundreds of meters wide) are never found with present-day volcanic chambers in this form and size?  Were the magmas of that time (the Turkish silica deposits extended from the Paleozoic up to the Tertiary) different in some way from those of today?  Could these silicious outpourings and the water-containing, colloidal conditions being considered here for certain serpentinites be somehow connected, in that certain magmatic processes were at that time so water-rich or high in silicic acid content, that during their solidification they led on the one hand to serpentinite forms resembling gel-phenomena, and on the other to significant silicious outpourings? In the chapter dealing with agates, a phenomenon will be discussed which leads to similar conjectures: the agate-forming magmas were, during or after their solidification, high in silicious acid content, and formed larges drops of silica gel.