Carbonate minerals

(mineralogy) A mineral containing considerable amounts of carbonates.

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Mineral species containing the carbonate ion as the fundamental anionic unit. The carbonate minerals can be classified as (1) anhydrous normal carbonates, (2) hydrated normal carbonates, (3) acid carbonates (bicarbonates), and (4) compound carbonates containing hydroxide, halide, or other anions in addition to the carbonate.

Most of the common carbonate minerals belong to group (1), and can be further classified according to their structures. The rhombohedral carbonates are typified by calcite, CaCO₃, and by dolomite, CaMg(CO₃)₂, The other structural type within this group is that of aragonite, which has orthorhombic symmetry. See also Ankerite; Aragonite; Calcite; Cerussite; Dolomite; Magnesite; Rhodochrosite; Siderite; Smithsonite; Strontianite; Witherite.

The minerals in groups (2) and (3) all decompose at relatively low temperatures and therefore occur only in sedimentary deposits (typically evaporites) and as low-temperature hydrothermal alteration products. The only common mineral in these groups is trona, Na₃H(CO₃)₂ · 2H₂O.

Similarly, the group (4) minerals are relatively rare and are characteristically low-temperature hydrothermal alteration products. The commonest members of this group are malachite, Cu₂CO₃(OH)₂, and azurite, Cu₃(CO₃)₂(OH)₂, which are often found in copper ore deposits. See also Azurite; Malachite.

Important occurrences of carbonates include ultrabasic igneous rocks such as carbonatites and serpentinites, and metamorphosed carbonate sediments, which may recrystallize to form marble. The major occurrences of carbonates, however, are in sedimentary deposits as limestone and dolomite rock. See also Dolomite rock; Limestone; Marble; Sedimentary rocks.

Carbonate minerals are those minerals containing the carbonate ion: CO₃^2-.

Contents 1 Carbonate classes 1.1 Anhydrous carbonates 1.2 Anhydrous carbonates with compound formulas 1.3 Carbonates with hydroxyl or halogen 1.4 Hydrated carbonates 2 References

Carbonate classes

Anhydrous carbonates

• Calcite group: Trigonal
  • Calcite CaCO₃
  • Gaspeite (Ni,Mg,Fe²⁺)CO₃
  • Magnesite MgCO₃
  • Otavite CdCO₃
  • Rhodochrosite MnCO₃
  • Siderite FeCO₃
  • Smithsonite ZnCO₃
  • Sphaerocobaltite CoCO₃
• Aragonite group: Orthorhombic
  • Aragonite CaCO₃
  • Cerussite PbCO₃
  • Strontianite SrCO₃
  • Witherite BaCO₃
  • Rutherfordine UO₂CO₃
  • Natrite Na₂CO₃

Anhydrous carbonates with compound formulas

• Dolomite group: Trigonal
  • Ankerite CaFe(CO₃)₂
  • Dolomite CaMg(CO₃)₂
  • Minrecordite CaZn(CO₃)₂
  • Barytocite BaCa(CO₃)₂

Carbonates with hydroxyl or halogen

Malachite

• Carbonate with hydroxide: Monoclinic
  • Azurite Cu₃(CO₃)₂(OH)₂
  • Hydrocerussite Pb₃(CO₃)₂(OH)₂
  • Malachite Cu₂CO₃(OH)₂
  • Roassite (Cu,Zn)₂CO₃(OH)₂
  • Phosgenite Pb₂(CO₃)Cl₂
  • Hydrozincite Zn₅(CO₃)₂(OH)₆
  • Aurichalcite (Zn,Cu)₅(CO₃)₂(OH)₆

Hydrated carbonates

• Ikaite CaCO₃.6(H₂O)
• Lansfordite MgCO₃·5(H₂O)
• Monohydrocalcite CaCO₃.H₂O
• Natron Na₂CO₃·10(H₂O)
• Zellerite Ca(UO₂)(CO₃)₂·5(H₂O)

The carbonate class in both the Dana and the Strunz classification systems includes the nitrates, the borates, and the iodates.

References

• Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0-471-80580-7
• Webmineral Dana Classification

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