Carbonates are a class of minerals whose basic structural unit is the carbonate anion, which most often forms compounds with calcium, magnesium, iron, manganese, zinc, copper, lead, or rare-earth elements. Carbonate minerals are generally of low hardness, soluble in hydrochloric acid, and exhibit distinct anisotropy in many physical properties, a result of the planar structure of the carbonate anion group. A specific example of anisotropy is double refraction, where light passing through a crystal is split into two beams because the speed of light varies in different directions. Double refraction is very noticeable in transparent calcite crystals, which are commonly found in Iceland and are hence referred to as Iceland spar.

Carbonates are very widespread in the Earth's crust, and the most important among them are calcite and dolomite, which form large monomineralic rock masses of sedimentary origin, i.e., limestone and dolomite rocks. These rocks are characterized by karst phenomena, including cave formations such as speleothems (stalagmites, stalactites, etc.), which are also made of carbonate minerals. Many other carbonates are much rarer and do not have significant petrographic importance.

In addition to calcite and dolomite, other notable carbonate minerals include magnesite, rhodochrosite, siderite, smithsonite, aragonite, cerussite, strontianite, witherite, ankerite, and natron (soda). Some of them are ore minerals, such as siderite (iron ore), rhodochrosite (manganese ore), smithsonite (zinc ore), and cerussite (lead ore). Among carbonates, there are also minerals used in gemology, such as malachite and azurite, which have been used as pigments for centuries due to their distinctive colors.