Metasomatism

When metasomatism (Greek μετα ( meta), with, after, to -' and σῶμα ( SOMA ), body ') or displacement is replaced, the material of a rock or stone of certain components by other material. In this way, pseudomorphs of minerals can occur. The metasomatism represents a limiting case of metamorphosis, since they generally do not expire ISOCHEM. In contrast to the isochemical metamorphism in the metasomatism that is, the elementary chemical composition of the rock is changed ( allochemische metamorphosis ).

Metasomatic processes take place the differentiation of magmas, especially in the embossed by pneumatolytic and hydrothermal processes final stages. The rock is attacked here by more or less hot, aggressive fluids. The existing minerals react with the dissolved substances in the fluids to other minerals.

A typical metasomatisches rock is the skarn, the alkali metasomatism arise when supplied with K-feldspar and albite, potassium and sodium, a typical process. The alkali metasomatism plays an important role in the Granitisation mentioned emergence of granite -like rocks from non- feldspar granites as greywacke or paragneisses, in which the newly formed feldspar crystals displace the original rock, more or less. This process leads, for example the formation of augen gneiss.

Even fossils can be caused by metasomatism. Examples are silicified wood or hard parts, their original material ( usually calcite or aragonite ) dissolved and replaced by another, eg by silica such as quartz, chalcedony and opal ( silicification ) or sulfides such as pyrite or marcasite ( Verkiesung ).