1. Is it possible for alkali feldspar to alter to sericite by another process that is not SERICITIC ALTERATION?
2. Does presence of sericitic alteration indicate subsolidus reactions of alkali feldspar with hydrothermal fluids?
'sericite' is a fine-grained variety of muscovite. 'sericite' is an alteration product of various aluminosilicate minerals. 'sericite' can also contain a lot of illite.
Sericitization of alkali feldspar occurs both during metasomatic-hydrothermal and during auto-hydrothermal processes, as well as during (retrograde) metamorphic processes.
Best regards,
Guenter Grundmann
Dear Kayode, yes there is another process which could replace potassic feldspar by fine-grained sericite-epidote assemblages. It is called saussuritization. Typically, it affects plagioclase phases, but it can also overprint potassic feldspars. Cheers Daniel
Dear Dr. Amuda
Sericite is a common term to describe only the grain size of white mica-type clay minerals encompassing muscovite, Na-K illite, and paragonite which stands for a wide range of lithological processes documented below:
Muscovite can be present as a hydrothermal phyllosilicate in many mineral deposits and it is stable under HT and HP metamorphic conditions up to 700°C depending on the lithostatic pressure in progressive and retrograde processes.
Paragonite is present under Na enriched regimes. In case of a contact paragenesis of albite or Na-enriched plagioclase and pyrophyllite paragonite comes into existence.
Illite or its Na analogue brammallite are common products of weathering of plagioclase s.s.s. but come into being also under hydrothermal conditions (see Füzérradvány, Tokaj Mts., Hungary).
With kind regards
H.G.Dill
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