Muscovite formed by regional metamorphism

The characteristics of the element partitioning indicate that the dendritic portion was formed rapidly and over a short period this element partitioning is principally controlled by the thermodynamics, i.e. the temperature and pressure, whereas the growth of the core portion and the growth sectors are by the layer growth mechanism, and the element partitioning is principally controlled by the kinetics. 

When a crystal is formed and becomes large in the mother sedimentary rocks metamorphosed, by contact metasomatism, crystals with similar textures are often formed. Chiastolite, a form of andalusite (Al SiO ) with a particular texture, may be such an example. 

Regional metamorphism proceeds in a wide area, and characteristic mineral paragenesis appears in zones depending on the temperature and pressure conditions that were confronted by the original rock. These are called metamorphic 

Sunagawa and Y. Koshino, Growth spirals on kaolin group minerals.Atn. Min., 60. 1975,407-12 

Sunagawa, Y. Koshino, M. Asakura, and T. Yamamoto. Growth mechanism of some clay minerals, Fortschr. Min., 52,1975, 515-20 

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