Ferrogedrite is an

amphibole Amphibole () is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is A ...

mineral with the complex chemical formula of ☐Fe²⁺₂(Fe²⁺₃Al₂)(Si₆Al₂)O₂₂(OH)₂. It is sodium and calcium poor, making it part of the

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...

lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid el ...

amphibole subgroup. Defined as less than 1.00 apfu (atoms per formula unit) of Na + CaLeake, B. (2004) Nomenclature of amphiboles: Additions and revisions to the International Mineralogical Association’s amphibole nomenclature. American Mineralogist. 89. 883-88

and consisting of greater than 1.00 apfu of (Mg, Fe²⁺, Mn²⁺, Li) separating it from the calcic-sodic amphiboles.Deer, William Alexander, Robert Andrew Howie, and Jack Zussman. Rock-forming minerals. 2B. Double-chain silicates. Vol. 2. Geological Society, 1997. It is related to

anthophyllite Anthophyllite is an orthorhombic amphibole mineral: ☐Mg2Mg5Si8O22(OH)2 (☐ is for a vacancy, a point defect in the crystal structure), magnesium iron inosilicate hydroxide. Anthophyllite is polymorphic with cummingtonite. Some forms of anthoph ...

amphibole and

gedrite Gedrite is a crystal belonging to the orthorhombic ferromagnesian subgroup of the amphibole supergroup of the double chain inosilicate minerals with the ideal chemical formula . Gedrite is the magnesium (Mg) rich endmember of a solid solution ser ...

through

coupled substitution Coupled substitution is the geological process by which two Chemical element, elements simultaneous substitute into a crystal in order to maintain overall electrical neutrality and keep the charge constant. In forming a solid solution series, Io ...

of (Al, Fe³⁺) for (Mg, Fe²⁺, Mn) and Al for Si. and determined by the content of silicon in the

standard cell In semiconductor design, standard cell methodology is a method of designing application-specific integrated circuits (ASICs) with mostly digital-logic features. Standard cell methodology is an example of design abstraction, whereby a low-level v ...

Occurrence

Specimens of ferrogedrite have been collected in the

greenstone belt Greenstone belts are zones of variably metamorphosed mafic to ultramafic volcanic sequences with associated sedimentary rocks that occur within Archaean and Proterozoic cratons between granite and gneiss bodies. The name comes from the green ...

of Africa, in the mountains of Norway, Greenland, Japan and in amphibole specimens from northwest America as well as the southern coast of California. Ferrogedrite exists in low temperature, high pressure

contact metamorphic 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 chem ...

geologic settings and remain stable up to 600 °C-800 °C due to its iron content.

Structure

As an end member of its subgroup due to its aluminium content in the octahedral site, is sensitive to high pressures. The M4 site is the most important for classification housing the largest cation and causing behavior similar to

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...

amphiboles. The linear relationship between the radius of M4 cations and the grand mean radius is varied and dependent on the M1, M2, and M3 sites inferring reliance on aluminium. The maximum content of aluminium in Ferrogedrite is 1.47 in the octahedral site. A low-temperature

solvus In a physical or geochemical system, a solvus is a line (binary system) or surface (ternary system) on a phase diagram which separates a homogeneous solid solution from a field of several phases which may form by exsolution or incongruent melting. ...

in the mineral causes exsolution changing the chemistry of a specimen resulting in confusing variations and close peaks in the diffraction pattern due to overlapping of phases. Ferrogedrite is an

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a r ...

dipyramidal amphibole with an H-M symbol of 2/m 2/m 2/m, and its space group is Pnma. Cleavage is perfect, indistinct, and indistinct with angles not at 90 degrees.Nesse, W.D. (2011) ''Introduction to Mineralogy,'' Oxford University Press, Created by distinct events, exsolution during cooling suggests its structure can be in

asbestos Asbestos () is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre being composed of many microscopic "fibrils" that can be released into the atmosphere b ...

form. This is a hydrous mineral that will exsolve and form course, elongated laths (230–1070 mm, or fine fibrous (10–70 mm). This double chain inosilicate with two unequal double-chains of tetrahedral the A and B chains. The Fe²⁺ are smaller cations in the M4 site than monoclinic amphiboles rich in Na and Ca and results in weakness under pressure. The higher Al content of the mineral strengthens the mineral as it increases the size of the tetrahedral and its placement in the M2 site. The rigidity of Al in the mineral counteracts the compressional weakness of the Fe²⁺ in high temperature and pressure environments. It is believed the edge-sharing ribbon of octahedra provides the strength and resistance to the structure.

Properties

Ferrogedrite is identified optically by its distinct cleavage and twinning with angles wider (650 and 1330)Law, A. (1982) Studies of the orthoamphiboles III. Hydroxyl Spectra of gedrites. Mineral Magazine 45. 63-71 http://www.minersoc.org/pages/Archive-MM/Volume_45/45-337-63.pdf than its counterparts, its dark-green to brown rims. and minor matrix. The hardness of ferrogedrite registers between 5.5-5.6 on the Mohs hardness scale and will scratch a knife blade and leaves a gray white streak on a ceramic plate. Ferrogedrite in its fibrous state, along with other amphiboles is considered due to medium-grade conditions. Found initially by Seki and Yamasaki in 1957 in Japan and approved by the IMA in 1978. It is often found as an inclusion in

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different s ...

crystals.Boniface, N. (2011
''Contact Metamorphism in the Supracrustal rocks of the Sukamaland Greenstone belt in the Northwest Tanzania
'' Tanzania Journal of Science. 37. 1. 1-12

References

{{reflist Amphibole group Orthorhombic minerals Minerals in space group 62