'Mineral hydration' is an inorganic chemical reaction where water is added to the
crystal structure of a
mineral, usually creating a new mineral, usually called a ''
hydrate''.
In
geological terms, the process of mineral hydration is known as
metasomatism, or ''alteraion'' and is a process occurring in
retrograde metamorphism. Hydration of minerals occurs generally in concert with
hydrothermal circulation.
Mineral hydration is also a process in the
regolith via conversion of silicate minerals into
clay minerals.
There are two main ways in which minerals hydrate. One is conversion of an
oxide to a double
hydroxide, as in the hydration of
calcium oxide - CaO - to
calcium hydroxide - Ca(OH)
2, the other is incorporation of water molecules directly into the crystalline structure of the mineral, as in the hydration of
feldspars to
clay minerals.
Some mineral structures, for example,
montmorillonite, are capable of including a variable amount of water without significant change to the mineral structure.
Hydration is the mechanism by which
Portland cement develops strength.
See also
★
Metasomatism
★
Metamorphism
★
Hydrothermal circulation