inorganic chemistry Inorganic chemistry deals with chemical synthesis, synthesis and behavior of inorganic compound, inorganic and organometallic chemistry, organometallic compounds. This field covers chemical compounds that are not carbon-based, which are the subj ...

, mineral hydration is a reaction which adds water to the

crystal structure In crystallography, crystal structure is a description of ordered arrangement of atoms, ions, or molecules in a crystalline material. Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that repeat ...

of a

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

, usually creating a new mineral, commonly called a ''

hydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

''. In

geological Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth s ...

terms, the process of mineral hydration is known as ''retrograde alteration'' and is a process occurring in

retrograde metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of c ...

. It commonly accompanies

metasomatism Metasomatism (from the Greek μετά ''metá'' "change" and σῶμα ''sôma'' "body") is the chemical alteration of a rock by hydrothermal and other fluids. It is traditionally defined as metamorphism which involves a change in the chemical com ...

and is often a feature of wall rock alteration around ore bodies. Hydration of minerals occurs generally in concert with

hydrothermal circulation Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

, which may be driven by

tectonic Tectonics ( via Latin ) are the processes that result in the structure and properties of the Earth's crust and its evolution through time. The field of ''planetary tectonics'' extends the concept to other planets and moons. These processes ...

or igneous activity.

Processes

There are two main ways in which minerals hydrate. One is conversion of an

oxide An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...

to a double

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It ...

, as with the hydration of

calcium oxide Calcium oxide (formula: Ca O), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term '' lime'' connotes calcium-containing ...

—CaO—to

calcium hydroxide Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca( OH)2. It is a colorless crystal or white powder and is produced when quicklime ( calcium oxide) is mixed with water. Annually, approxim ...

—Ca(OH)₂. The other is with the incorporation of water molecules directly into the crystalline structure of a new mineral, as with the hydration of

feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...

s to

clay mineral Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay minera ...

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. Garnet minerals, while sharing similar physical and crystallographic properties, exhibit a wide range of chemical compositions, de ...

chlorite The chlorite ion, or chlorine dioxide anion, is the halite (oxyanion), halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as s ...

, or

kyanite Kyanite is a typically blue aluminosilicate mineral, found in aluminium-rich metamorphic pegmatites and sedimentary rock. It is the high pressure Polymorphism (materials science), polymorph of andalusite and sillimanite, and the presence of kyani ...

muscovite Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated phyllosilicate mineral of aluminium and potassium with formula KAl2(Al Si3 O10)( F,O H)2, or ( KF)2( Al2O3)3( SiO2)6( H2O). It has a highly perfect basal cleavage y ...

. Mineral hydration is also a process in the regolith that results in conversion of silicate minerals into

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

minerals. Some mineral structures, for example,

montmorillonite Montmorillonite is a very soft phyllosilicate group of minerals that form when they precipitate from water solution as microscopic crystals, known as clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite grou ...

, are capable of including a variable amount of water without significant change to the mineral structure. Hydration is the mechanism by which hydraulic binders such as

Portland cement Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar (masonry), mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in th ...

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 In chemical physics and physical chemistry, chemical affinity is the electronic property by which dissimilar chemical species are capable of forming chemical compounds. Chemical affinity can also refer to the tendency of an atom or compound to com ...

of the hydration reaction.

Examples of hydrated minerals

Examples of hydrated minerals include: *

silicate A silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is also used ...

s (, ) **

phyllosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, the crystalline forms of silica (silicon dio ...

s, clay minerals "commonly found on Earth as weathering products of rocks or in

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

systems" ***

***

* non-silicates ** oxides (, , , etc.) and oxy-hydroxides ***

brucite Brucite is the mineral form of magnesium hydroxide, with the chemical formula Magnesium, Mg(hydroxyl, OH)2. It is a common alteration product of periclase in marble; a low-temperature hydrothermal Vein (geology), vein mineral in metamorphosed li ...

, ***

goethite Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the α- polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient t ...

, FeO(OH) **

carbonate A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group ...

s (, etc.) ***

hydromagnesite Hydromagnesite is a hydrated magnesium carbonate mineral with the formula . It generally occurs associated with the weathering products of magnesium containing minerals such as serpentine group, serpentine or brucite. It occurs as incrustations a ...

, *** ikaite, , the unstable hexahydrate form of calcium carbonate ** hydroxylated minerals ***

saponite Saponite is a trioctahedral mineral of the smectite group. Its chemical formula is . It is soluble in sulfuric acid. It was first described in 1840 by Lars Fredrik Svanberg, Svanberg. Varieties of saponite are griffithite, bowlingite and sobotk ...

***

talc Talc, or talcum, is a clay mineral composed of hydrated magnesium silicate, with the chemical formula . Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent and lubricant ...

** hydroxysulfides (mixed sulfides-hydroxides) *** tochilinite, a hydroxysulfide or hydrated

sulfide Sulfide (also sulphide in British English) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to large families o ...

mineral of iron(II) and magnesium of chemical formula:
, also written , in IMA notation *** valleriite, an uncommon sulfide-hydroxide mineral of iron(II) and copper of chemical formula:
,Valleriite on Mindat.org
/ref> or {{chem2, 4 (Fe,Cu)S * 3 (Mg,Al)(OH)2Handbook of Mineralogy
/ref>

References

Metamorphic petrology * Inorganic reactions es:Hidratación mineral

Processes

Examples of hydrated minerals

See also

References