Mineral hydration is an inorganic chemical reaction where water is added to the
crystal structureIn mineralogy and crystallography, a crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a motif, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
of a
mineralA mineral is a naturally occurring solid formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties. A rock, by comparison, is an aggregate of minerals and/or mineraloids, and need not have a specific...
, usually creating a new mineral, usually called a
hydrateHydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....
.
In
geologicalGeology is the science and study of the solid and liquid matter that constitutes the Earth. The field of geology encompasses the study of the composition, structure, physical properties, dynamics, and history of Earth materials, and the processes by which they are formed, moved, and changed...
terms, the process of mineral hydration is known as
metasomatismMetasomatism is the chemical alteration of a rock by hydrothermal and other fluids.Metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source. In the igneous environment, metasomatism creates skarns, greisen, and may affect hornfels in the contact...
, or
alteraion and is a process occurring in retrograde metamorphism. Hydration of minerals occurs generally in concert with
hydrothermal circulationHydrothermal circulation in its most general sense is the circulation of hot water; 'hydros' in the Greek meaning water and 'thermos' meaning heat. Hydrothermal circulation occurs most often in the vicinity of sources of heat within the Earth's crust...
.
Mineral hydration is also a process in the
regolithRegolith is a layer of loose, heterogeneous material covering solid rock. The term is a combination of two Greek words: Rhegos , which means blanket, and Lithos , which means rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids,...
via conversion of silicate minerals into
clayClay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired...
minerals.
There are two main ways in which minerals hydrate.
Mineral hydration is an inorganic chemical reaction where water is added to the
crystal structureIn mineralogy and crystallography, a crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a motif, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
of a
mineralA mineral is a naturally occurring solid formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties. A rock, by comparison, is an aggregate of minerals and/or mineraloids, and need not have a specific...
, usually creating a new mineral, usually called a
hydrateHydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....
.
In
geologicalGeology is the science and study of the solid and liquid matter that constitutes the Earth. The field of geology encompasses the study of the composition, structure, physical properties, dynamics, and history of Earth materials, and the processes by which they are formed, moved, and changed...
terms, the process of mineral hydration is known as
metasomatismMetasomatism is the chemical alteration of a rock by hydrothermal and other fluids.Metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source. In the igneous environment, metasomatism creates skarns, greisen, and may affect hornfels in the contact...
, or
alteraion and is a process occurring in retrograde metamorphism. Hydration of minerals occurs generally in concert with
hydrothermal circulationHydrothermal circulation in its most general sense is the circulation of hot water; 'hydros' in the Greek meaning water and 'thermos' meaning heat. Hydrothermal circulation occurs most often in the vicinity of sources of heat within the Earth's crust...
.
Mineral hydration is also a process in the
regolithRegolith is a layer of loose, heterogeneous material covering solid rock. The term is a combination of two Greek words: Rhegos , which means blanket, and Lithos , which means rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids,...
via conversion of silicate minerals into
clayClay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired...
minerals.
There are two main ways in which minerals hydrate. One is conversion of an
oxideAn oxide is a chemical compound containing at least one oxygen atom as well as at least one other element. Most of the Earth's crust consists of oxides. Oxides result when elements are oxidized by oxygen in air. Combustion of hydrocarbons affords the two principal oxides of carbon, carbon...
to a double
hydroxideIn chemistry, hydroxide is the name for the diatomic anion OH−, consisting of oxygen and hydrogen atoms, usually derived from the dissociation of a base. It is one of the simplest diatomic ions known....
, as in the hydration of
calcium oxideCalcium oxide , commonly known as burnt lime, lime or quicklime, is a widely used chemical compound. It is a white, caustic and alkaline crystalline solid at room temperature. As a commercial product, lime often also contains magnesium oxide, silicon oxide and smaller amounts of aluminium oxide and...
- CaO - to
calcium hydroxideCalcium hydroxide, traditionally called slaked lime, hydrated lime, slack lime, or pickling lime, is a chemical compound with the chemical formula Ca2. It is a colourless crystal or white powder, and is obtained when calcium oxide is mixed, or "slaked" with water...
- Ca(OH)
2, the other is incorporation of water molecules directly into the crystalline structure of the mineral, as in the hydration of
feldsparFeldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
s to clay minerals.
Some mineral structures, for example,
montmorilloniteMontmorillonite is a very soft phyllosilicate group of minerals that typically form in microscopic crystals, forming a clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite family, is a 2:1 clay, meaning that it has 2 tetrahedral sheets sandwiching a central...
, are capable of including a variable amount of water without significant change to the mineral structure.
Hydration is the mechanism by which
Portland cementPortland cement is the most common type of cement in general use around the world, because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...
develops strength.