(1) (n.) Geology. A class of sedimentary rock whose chief mineral constituents (95% or more) are calcite and aragonite (both CaCo₃) and dolomite [CaMg(CO₃)₂], a mineral that can replace calcite during the process of dolomitization. Limestone, dolostone or dolomite, and chalk are carbonate rocks. Although carbonate rocks can be clastic in origin, they are more commonly formed through processes of precipitation or the activity of organisms such as coral and algae. Carbonates form in shallow and deep marine settings, evaporitic basins, lakes and windy deserts. Carbonate rocks can serve as hydrocarbon reservoir rocks, particularly if their porosity has been enhanced through dissolution. They rely on fractures for permeability. See: chert, clasticsediment, karst, micrite, reef, reservoir, siliciclastic sediment, stylolite. More Details: Confronting the Carbonate Conundrum. (2) (adj.) Geology. A group of minerals found mostly in limestone and dolostone that includes aragonite, calcite and dolomite. Calcite is the most abundant and important of the carbonate minerals. See: dolomitization, evaporite, humic acid, micrite, reef, siderite, sour gas. More Details: Confronting the Carbonate Conundrum