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14.7: Carbonates and Nitrates

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    Mineralogists divide carbonate minerals into three main groups based on atomic arrangement: the calcite group, dolomite group, and aragonite group. Several other species that have more complex structures and chemistries are classified separately.

    Calcite group minerals have hexagonal structures related to the structures of halite and galena: six Ca, Mg, Fe, Mn, or Zn surround anionic (CO3)-2 groups and each metal atom is surrounded by six carbonate groups. Dolomite group minerals have structures similar to calcite’s, but Ca and Mg, Fe, or Mn occupy alternate layers. Aragonite group minerals are orthorhombic. Solid solutions are common within a structural group, although some carbonates, such as aragonite, are almost always close to end-member composition.

    Calcite Group
    calcite CaCO3
    magnesite MgCO3
    siderite FeCO3
    rhodochrosite MnCO3
    smithsonite ZnCO3

    Dolomite Group
    dolomite CaMg(CO3)2
    ankerite CaFe(CO3)2
    kutnahorite CaMn(CO3)2

    Aragonite Group
    aragonite CaCO3
    witherite BaCO3
    strontianite SrCO3
    cerussite PbCO3

    Other Carbonates
    malachite Cu2CO3(OH)2
    azurite Cu3(CO3)2(OH)2

    Nitrate Group
    nitratite NaNO3
    niter (saltpeter) KNO3

    Due to very high solubility in water, nitrate minerals are rare. They have structures similar to carbonates, but contain monovalent rather than divalent cations because the (NO3) anionic group is monovalent. Over half a dozen nitrates are known, but nitratite and niter are the only common ones in more than just a few localities.

    For more general information about carbonates and nitrates, see Section 7.4.3 of Chapter 7.

    This page titled 14.7: Carbonates and Nitrates is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Dexter Perkins via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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