Fougerite
Encyclopedia
Fougerite is a recently discovered representative of clay minerals
Clay minerals
Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations. Clays have structures similar to the micas and therefore form flat hexagonal sheets. Clay minerals are common weathering products and low...

, chemically and structurally related to so-called green rust, hydrotalcite-like minerals (hydrotalcite
Hydrotalcite
Hydrotalcite is a layered double hydroxide of general formula Hydrotalcite is a layered double hydroxide of general formula Hydrotalcite is a layered double hydroxide of general formula (Mg6Al2(CO3)(OH)16·4(H2O) whose name is derived from its resemblance with talc and its high water content. It is...

, pyroaurite, iowaite, manasseite) and other layered double hydroxides
Layered double hydroxides
Layered double hydroxides comprise an unusual class of layered materials with positively charged layers and charge balancing anions located in the interlayer region. This is unusual in solid state chemistry: many more families of materials have negatively charged layers and cations in the...

. The formula of the mineral is complex due to structural variabilities, as is for green rust, thus different formulas can be found elsewhere. The structure is based on brucite
Brucite
Brucite is the mineral form of magnesium hydroxide, with the chemical formula Mg2. It is a common alteration product of periclase in marble; a low-temperature hydrothermal vein mineral in metamorphosed limestones and chlorite schists; and formed during serpentinization of dunites...

-like layers. Fougerite crystallizes in trigonal system. The originally given formula for fougerite is [Fe2+1-xFe3+xMgy(OH)2+2y]+x[x/n A-n.mH2O]-x where A denotes an interlayer anion, n denotes valency, by 1/4 ≤ x/(1+y) ≤ 1/3 and m ≤ (1-x+y) (Trolard et al. 2007).

The interlayer anions may be OH-, Cl-, CO32-, SO42- and other. Fougerite is unique among other clay minerals
Clay minerals
Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations. Clays have structures similar to the micas and therefore form flat hexagonal sheets. Clay minerals are common weathering products and low...

 due to having a positive layer charge.

Fougerite was found in forested soils near Fougères
Fougères
Fougères is a commune and a sub-prefecture of the Ille-et-Vilaine department in Brittany, in north-western France.-Sights:Fougères' major monument is a medieval stronghold built atop a granite ledge, which was part of the ultimately unsuccessful defence system of the Duchy of Brittany against...

 (Brittany
Brittany
Brittany is a cultural and administrative region in the north-west of France. Previously a kingdom and then a duchy, Brittany was united to the Kingdom of France in 1532 as a province. Brittany has also been referred to as Less, Lesser or Little Britain...

, France). It possess blue-green to bluish-gray colour. It is regarded as a precursor for other iron hydroxides and related compounds, like goethite
Goethite
Goethite , named after the German polymath Johann Wolfgang von Goethe, is an iron bearing oxide mineral found in soil and other low-temperature environments. Goethite has been well known since prehistoric times for its use as a pigment. Evidence has been found of its use in paint pigment samples...

, lepidocrocite
Lepidocrocite
Lepidocrocite , also called esmeraldite or hydrohematite, is an iron oxide-hydroxide mineral. Lepidocrocite has an orthorhombic crystal structure, a hardness of 5, specific gravity of 4, a submetallic luster and a yellow-brown streak. It is red to reddish brown and forms when iron-containing...

 and ferrihydrite
Ferrihydrite
Ferrihydrite is a widespread hydrous ferric oxyhydroxide mineral at the Earth's surface, and a likely constituent in extraterrestrial materials. It forms in several types of environments, from freshwater to marine systems, aquifers to hydrothermal hot springs and scales, soils, and areas affected...

 (Trolard et al. 2007, Génin et al. 2005).

See also

  • Clay minerals
    Clay minerals
    Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations. Clays have structures similar to the micas and therefore form flat hexagonal sheets. Clay minerals are common weathering products and low...

  • Gley soil
    Gley soil
    Gley soil in soil science is a type of hydric soil which exhibits a greenish-blue-grey soil color due to wetland conditions. On exposure to the air, gley colors are transformed to a mottled pattern of reddish, yellow or orange patches. During gley soil formation , the oxygen supply in the soil...

  • Iron(II) hydroxide
    Iron(II) hydroxide
    Iron hydroxide or ferrous hydroxide is a compound produced when iron ions, from a compound such as iron sulfate, react with hydroxide ions. Iron hydroxide itself is practically white, but even traces of oxygen impart it with a greenish tinge...

  • Layered double hydroxides
    Layered double hydroxides
    Layered double hydroxides comprise an unusual class of layered materials with positively charged layers and charge balancing anions located in the interlayer region. This is unusual in solid state chemistry: many more families of materials have negatively charged layers and cations in the...

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