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The partial or complete replacement of pre-existing plagioclase or alkali feldspar by albite. There are a number of ways in which this can be achieved. A common process involves the residual water-rich vapour released during the final stages of crystallization of a granite body. This vapour, which can carry high concentrations of Na+ in solution, rises through the granite body and reacts with the feldspars present in the granite, converting them to albite which is stable under the lower temperature vapour-rich conditions. A typical reaction that partially or completely replaces plagioclase would be: CaAl2Si2O8 + 4SiO2 + 2Na+ → 2NaAlSi3O8 + Ca2+; anorthite + quartz + sodium (in aqueous solution) → albite + calcium (in aqueous solution). This type of reaction, where a rock simmers in its own juices, is termed a ‘deuteric reaction’. Another way in which albitization can be achieved is by the reaction of ocean-floor basalts with sea water in thermal circulation cells within the basalt layer of the oceanic crust.

Subjects: Earth Sciences and Geography.

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