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Mineral hydration

Chemical reaction adding water to a mineral's crystal structure From Wikipedia, the free encyclopedia

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In inorganic chemistry, mineral hydration is a reaction which adds water to the crystal structure of a mineral, usually creating a new mineral, commonly called a hydrate.

In geological terms, the process of mineral hydration is known as retrograde alteration and is a process occurring in retrograde metamorphism. It commonly accompanies metasomatism and is often a feature of wall rock alteration around ore bodies. Hydration of minerals occurs generally in concert with hydrothermal circulation, which may be driven by tectonic or igneous activity.

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Processes

There are two main ways in which minerals hydrate. One is conversion of an oxide to a double hydroxide, as with the hydration of calcium oxide—CaO—to calcium hydroxide—Ca(OH)2. The other is with the incorporation of water molecules directly into the crystalline structure of a new mineral,[1] as with the hydration of feldspars to clay minerals, garnet to chlorite, or kyanite to muscovite.[citation needed]

Mineral hydration is also a process in the regolith that results in conversion of silicate minerals into clay minerals.[citation needed]

Some mineral structures, for example, montmorillonite, are capable of including a variable amount of water without significant change to the mineral structure.[citation needed]

Hydration is the mechanism by which hydraulic binders such as Portland cement develop strength. A hydraulic binder is a material that can set and harden submerged in water by forming insoluble products in a hydration reaction. The term hydraulicity or hydraulic activity is indicative of the chemical affinity of the hydration reaction.[2]

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Examples of hydrated minerals

Examples of hydrated minerals include:

  • silicates (SiO4−
    4    , SiO
    2    )
  • non-silicates
    • oxides (O2−
      , Al
      2      O
      3      , Fe
      2      O
      3      , etc.) and oxy-hydroxides
      • brucite, Mg(OH)2[1]
      • goethite, FeO(OH)[1]
    • carbonates (CO2−
      3      , etc.)
    • hydroxylated minerals
    • hydroxysulfides (mixed sulfides-hydroxides)
      • tochilinite, a hydroxysulfide or hydrated sulfide[1] mineral of iron(II) and magnesium of chemical formula:
        (Fe2+)5.4(Mg,Fe2+)5S6(OH)10,[3] also written 6 Fe0.9S · 5 (Mg,Fe2+)(OH)2,[4][3] in IMA notation
      • valleriite, an uncommon sulfide-hydroxide mineral of iron(II) and copper of chemical formula:
        (Fe2+,Cu)4(Mg,Al)3S4(OH,O)6,[5] or 4 (Fe,Cu)S · 3 (Mg,Al)(OH)2[6]
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See also

References

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