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.
Table of ContentsA. Introduction: The Rôle of Mineralogy in the Petrology of Sedimentary Carbonates.- B. Crystal Chemistry of Sedimentary Carbonate Minerals.- I. Calcite-Type Minerals (Rhombohedral Carbonates).- 1. Calcite and Isotypic Minerals.- a) Calcite.- b) Isotypes of Calcite.- 2. Superstructures Based on Calcite Pattern.- a) Regular Interstratifications.- ?) Dolomite.- ?) Norsethite.- b) Superstructures with Order in the Individual Cation Layer.- 3. Disordered Calcite-Type Structures.- a) Magnesian Calcites.- b) Calcium-Rich (Calcian) Dolomites.- 4. Iron-Bearing Rhombohedral Carbonates.- a) Siderites.- b) Iron-Bearing Dolomites or Ankerites.- II. Aragonite.- III. Miscellaneous Carbonates.- 1. Vaterite.- 2. Hydrous Carbonates and the Magnesite Problem.- a) Hydrous Magnesium Carbonates.- b) Cation Hydration and the Dehydration Barrier.- c) Hydrated Calcium Carbonates.- 3. Alkali-Bearing Carbonates.- C. The Polymorphism Calcite-Aragonite.- I. Stable Relationships.- Calcite and Aragonite-Type Structures in Systems Other than CaCO3.- II. The Metastable Occurrence of Aragonite in Aqueous Solutions at Normal Pressure.- 1. In the Absence of Bivalent Cations Other than Ca2+.- 2. The Influence of Bivalent Cations Other than Ca2+.- a) Large Cations, Notably Strontium.- b) Small Cations, Notably Magnesium.- 3. Interpretation of Different Growth Forms of Aragonite Oöids.- 4. The Formation of Calcite and Aragonite in Organisms.- 5. The Persistence and Transformation of Aragonite.- D. The System CaCO3 MgCO3.- I. The Dolomite Question.- II. Phase Relations in the Dry System.- III. Systems Involving Aqueous Solutions.- 1. Hydrothermal Syntheses of Dolomite.- 2. Arguments Against the Hydrothermal Origin of Many Dolomite Formations.- 3. The Solubility of Dolomite at 25° C.- 4. Magnesian Calcites in Aqueous Systems.- 5. “Dedolomitization”.- 6. Huntite.- IV. The Aqueous Synthesis of Norsethite, BaMg(CO3)2, a Model for Low-Temperature Dolomite Formation.- 1. General Statement.- 2. Experimental Norsethite Formation.- 3. The Mechanism of Norsethitization.- 4. Conclusions Regarding the Low-Temperature Formation of Dolomite.- E. Petrological Summary: Reaction Series Leading from Carbonate Sediments to Carbonate Rocks.- I. The Formation of Fresh-Water Limestones.- II. The Evolution of Marine Limestones.- III. Dolomitization.- References.