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and their identification obviates individual thermochemical studies
on every genus. The stability relations among sedimentary carbonate
minerals are now more or less well known. The common rock-forming
minerals cal cite and dolomite are indeed stable phases in the
pertinent systems. Most other carbonate minerals of similar
composition which are known to occur in the younger sediments are
metastable with respect to calcite, dolomite, and magnesite. This
implies that the sedimentation of carbon ates is determined only in
part by stability relations. Kinetic factors, which allow the
formation of metastable minerals, appear to be more important.
Although the diagenetic transformations leading to stable minerals
take place by virtue of thermodynamic requirements, the reac tions
themselves are triggered by kinetic factors as well. Some of the
reactions leading from metastable to stable carbonate assemblages
are susceptible to simulation in the laboratory; others (e. g.
dolomitization) appear to be so slow that they can be studied only
in analogous systems characterized by reasonable reaction rates. In
all attempts to explain the possible mechanisms of such reactions,
we must consider the crystal structures of the final products as
well as of the starting materials. This is another viewpoint from
which mineralogy is important to carbonate petrology, if we regard
the crystal chemistry of minerals as a part of mineralogy. A
certain parallelism with clay mineralogy suggests itself."
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