Detrital microcline and albite are commonly replaced diagenetically by chlorite in sandstones of the Visingsö Group (Upper Proterozoic, southern Sweden). Authigenic quartz and, in some cases, albite and illite are associated with the chlorite. The SEM examinations suggest that chloritization of feldspar has usually been preceded by dissolution of the replaced feldspar grain. Fe 2+ and Mg2+, which are needed for the chloritization, have partly been derived from the detrital Fe-Mg silicates (mainly biotite) Fe-oxide pigment and Fe-Ti oxide grains, whereas Si4+ and Al3+ are supplied mostly by the altered feldspars. The K+ released from microcline and Na- from albite were mostly incorporated in authigenic illite and albite, respectively.
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