Why the wealth of forms?

If one, as an experiment, excludes one's own prior knowledge an approaches the crystalline rocks without preconceptions, one is immediately struck by the richness of forms and the beautiful, colorful appearances.  The photos below show granites and gneisses, as well as related silicatic rocks (migmatites, quartzite).

Granite with a large orthoclase component                          Gneiss with biotite bands
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Rapakivi Granite, Finland                                                   Syenite with Garnets (red)
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Left: Anorthosite or syenite/larvikite with shimmering labradorite (plagioclase) feldspar crystals, Norway
Right: Granite with orthoclase feldspar crystals (+ ring-formed biotite inner layer), Black Forest, Germany
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Left: Porphyritic granite with orthoclase crystals (alkali feldspar), Spain
Right: Pegmatitic labradorite (anorthosite) with giant crystals and black biotite and hornblende tablets, Madagascar
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Gneiss (Orthogneiss), South Africa 

Gneiss (Paragneiss), Switzerland
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Left: Quartzite with chromite-bearing fuchsite (a form of mica), Norway
Right: Augen gneiss or paragneiss, Brazil
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Left: Paragneiss with flattened feldspar crystals, Brasil
Right: "Compressed" augen gneiss
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Migmatite with distinctive coloring                                     Migmatite, Brazil
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cMigmatite, India 

Migmatitic Gneis or Quarzite
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Syenite with blue sodalith 

Quarzite with blue dumortierite, Brasil
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Could this obvious phenomenon of multiplicity of forms and colorfulness be scientifically important?  In general, one sees that regular structure and colorfulness in nature is found above all in the realm of life.  And that there it is- speaking generally- water which, as a chemically- and physically mediating factor, allows for the differentiation into forms and colors.  Regions lacking water, such as the basalt layers of the earth's crust or the basalt deserts of the moon show little structure, individuality and color, even if metals and crystallization, among other factors, may bring about a certain weak structure and colorfulness (for example through light-colored plagioclase, green olivine or red garnet).  One would like to draw the conclusion:  Whatever the process of origin of the silicious rocks was, it must have posessed a chemically-strong structuring, self-organizing aspect.  And this leads to the likely conclusion that water was significantly involved.

One can think here of the distance between the present-day concepts and alternative possibilities of thought:

The present-day position of science is that granites, gneisses and various related types of rock as arising from the slow cooling of molten (magmatic) material, or through the deep burial or submergence of rock layers.  That is, they come either directly from a primary magma, with minerals built up as crystals around a seed point (i-type granite), or as sediments which, in plate-tectonic subduction zones, are more or less-strongly metamorphosed through pressure and warming or heating (s-type granite).  These sediments (limestones, shale, conglomerates, sand, clay etc.) are drawn down into great depths, pressed together and recrystallized under high pressure and increased temperature, in part melted, and subsequently deformed through forces of pressure and shearing.  To this picture may be added combinations with basaltic or even deeper material, water-related (hydrothermal) and other chemical processes as well as radioactivity-related reactions, which then result in the endless number of different rocks.  The granite-related rocks are those which contain a significantly higher percentage of quartz, which also results in their lighter color. One can only investigate the rocks in question in laboratory experiments in a restricted manner, for instance only in small quantities and over short time periods.  In the end, the mode of origin of the worldwide rock complexes must depend on the observation and comparison of a series of selected phenomena, and in the end decided in thought.

The question here is: Which phenomena will be selected and compared?  And which main direction of thought will be brought to the phenomena?  Do the laboratory phenomena and chemistry and physics of minerals stand in the foreground?  Or the phenomena of morphology (forms) in organic and inorganic substances?  A certain inner logic leads from the selected group of phenomena to a particular grouping of theses.  The morphological group of phenomena considered here lead with a certain inner necessity to the signs, followed here as a hypothesis, of a greater participation of water in the processes.

One can receive the impression that the wealth of forms and fullness of color in the silicatic rocks cannot have arisen simply from molten magmas which differentiated through density differences or partial crystallization, or from metamorphosed layering.  Certainly, melting or metamorphosis could lead to gneiss-like forms; certainly silicatic rocks have gone through warming or even intensive heating, but these processes alone are not really convincing explanations for the formation of the silicate rocks systems of the earth with their numerous individual characters and structures.

The rocks which most clearly arise "only" from molten and likewise water-poor magma, namely lava, basalt and basalt-related rocks, have a monotonous character.  To a lesser degree this is valid also for other quartz- and water-poor rocks at depth (peridotite, gabbro, etc), or for some of the rock types arising from volcanic processes (rhyolite, also porphyry, trachite, andesite, etc.)  Here thate can be a certain structure and color, to be sure, but often with a more accidental-looking, less firm or even porous character.

Without bringing the chemical and physical proceses described into question, one is nevertheless tempted to add to them starting conditions with higher water content, actually from a colloidal consistency.  Such a water content, which is not ruled out in present academic thinking, but tends to be restricted quantitatively, would then have been the basis for the stron self-organizing, structure- and color-forming processes.

In what form, however, could this water have played a role?  Most likely in both fee and bound form, and in sufficient quantity that the rock masses would have posessed a significantly higher openness to diffusion, as well as a greater plasticity, than one normally assumes.  In this way the known mineral formation and transformation could have taken place more easily and rapidly as can occur in almost water-free material.  In this case on could assume that a part of the water bound up at that time is still to be found in the present hydrogen and oxygen content of the minerals, and a still larger amount was released and diffused away, and became part of the water of the oceans and within the earth's crust.  One can also think about the possibility of a larger water content in connection with the facts that oxygen, seen chemically, makes up nearly 50% of the earth's crust, and that hydrogen is the most abudant element on those planets whose higher gravity has allowed them them to hold on to it.

Chemists may not find such ideas satisfying, since quantitative relationships and formulae are lacking.  The hypothesis is developed here out of the morphology, which would require a further step to develop a chemical precision.  If the conditions of the primeval earth did actually resemble that hypothetically assumed in later chapters (for example, see the chapter "Self-organization"), however, then a chemical precision would be difficult.  Then, during a long path of irreversible processes within substantail conditions which no longer exist, a chemistry would have prevailed which would hardly be understandable in the present calculating sense.

In this connection one can think of experiments with colloidal-like substances, where at the conclusion a completely hardened, dry substance with a charactristic structure remains; where the process is irreversible and therefore difficult to reconstruct.  Depending of the type of colloidal material begun with, this may become repellent to water after hardening (hydrophobic), and not suitable for an experimental repetition of the dehydration and hardening processes.  For a repetition a new colloidal substance must be provided.  Could this have been the case with particular silicatic rocks?  This question will be gone into in the next chapter.

Dried-out, originally gelatenous substances: rock-hard and hardly able to take up water again.

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