carbonaten

Carbonaten, or carbonates, are a class of minerals that contain the carbonate anion CO3^2− and one or more metal cations. The simplest formula is MCO3, though many carbonates have more complex compositions or occur as mixed-cation minerals. Calcite and aragonite are polymorphs of calcium carbonate (CaCO3); dolomite is CaMg(CO3)2. Other common carbonate minerals include siderite (FeCO3), magnesite (MgCO3), rhodochrosite (MnCO3), and smithsonite (ZnCO3).

Formation and occurrence: Carbonates form by precipitation from carbonate-rich waters, through biological carbonate production (shells and skeletons), or by hydrothermal activity. They dominate sedimentary carbonate rocks such as limestone and dolostone and can occur in metamorphic rocks as marble when limestone recrystallizes. Carbonate deposits are widespread and appear in marine, freshwater, and terrestrial settings, from shallow seas to caves and hydrothermal systems.

Properties: Carbonates commonly effervesce in dilute acid due to CO2 release. They exhibit a range of crystal systems, from rhombohedral to orthorhombic, and hardness values typically fall around 3 to 4 on the Mohs scale. Color and transparency vary widely among minerals, and many carbonates have distinct cleavage patterns and refractive properties.

Uses and significance: Limestone and dolostone are major sources of lime (CaO) and are widely used as building materials and as aggregates in cement. Carbonate minerals also occur as ore minerals and as pigments or fillers in various industries. Geologically, carbonates play a key role in the carbon cycle, sequestering and releasing CO2 through dissolution and precipitation over geological timescales.

See also: List of carbonate minerals; Calcite; Dolomite; Marble.