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ABSTRACT |
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Mineral transformations in the zones of
diagenesis and burial metamorphism are
directed towards more compact
structures, in response to the
increasing role of pressure, more than
any other factor, in the physico-chemical
environment. These are manifested by
mineral changes involving: (1)
dehydration—desilication; (2)
desilication, accompanied by change in
coordination state of Al from
tetrahedral to octahedral; (3)
transformation into denser polymorphs;
(4) increasing fixation of smaller
cations with stronger bonds in lieu of
bigger ions with weaker bonds; and (5)
devitrification of glass.
The analcite to albite transformation in
the burial metamorphic zone is herein
considered a dehydration-desilication,
rather than a dehydration-silicification
reaction. SiO2, once
released, tends to form quartz rather
than take part in silicification.
Quartz, having a relatively compact
crystal structure, is stable under the
prevailing physico-chemical conditions.
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