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.