Fayalite

Fayalite

Infobox mineral
name = Fayalite
category =
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formula = Iron silicate (Fe2SiO4)
molweight =
color = Pale yellow, amber and green
habit =
system = Orthorhombic
twinning =
cleavage = {010} moderate, {100} weak
fracture = Conchoidal
mohs = 6.5
luster = Vitreous
refractive = α = 1.827,
β = 1.869,
γ = 1.879
opticalprop =
birefringence =
pleochroism =
streak =
gravity = 4.392
density =
melt =
fusibility =
diagnostic =
solubility =
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Fayalite (Fe2SiO4) is the iron rich end-member of the olivine solid-solution series. In common with all minerals in the olivine group, fayalite crystallizes in the orthorhombic system (space group "Pbnm") with cell parameters "a" 4.82 Å, "b" 10.48 Å and "c" Å 6.09.

Iron rich olivine is a relatively common constituent of acidic and alkaline igneous rocks such as volcanic obsidians, rhyolites, trachytes and phonolites and plutonic quartz syenites where it is associated with amphiboles. It also occurs in medium-grade thermally metamorphosed iron-rich sediments.

Fayalite is stable with quartz at low pressures, whereas more magnesian olivine is not, because of the reaction olivine + quartz = orthopyroxene. Iron stabilizes the olivine + quartz pair. The pressure and compositional dependence of the reaction can be used to calculate constraints on pressures at which assemblages of olivine + quartz formed.

Fayalite can also react with oxygen to produce magnetite + quartz: the three minerals together make up the "FMQ" oxygen buffer. The reaction is used to control the fugacity of oxygen in laboratory experiments. It can also be used to calculate the fugacity of oxygen recorded by mineral assemblages in metamorphic and igneous processes.

References

* Deer, W. A., Howie, R. A., and Zussman, J. (1992). "An introduction to the rock-forming minerals (2nd ed.)". Harlow: Longman ISBN 0-582-30094-0


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Look at other dictionaries:

  • Fayalite — Catégorie IX : silicates[1] Fayalite Coso Hot Springs, Californie, États Unis (XX 1 mm) …   Wikipédia en Français

  • Fayalite — Fay al*ite (f[=a] al*[imac]t), n. [So called from the island Fayal.] (Min.) A black, greenish, or brownish mineral of the chrysolite group. It is a silicate of iron. [1913 Webster] …   The Collaborative International Dictionary of English

  • fayalite — ● fayalite nom féminin (de Fayal, nom propre) Silicate naturel de fer appartenant à la famille des péridots, orthorhombique …   Encyclopédie Universelle

  • fayalite — /fay euh luyt , fuy ah luyt/, n. Mineral. the iron end member of the olivine group, Fe2SiO4. [1835 45; named after FAYAL; see ITE1] * * *       iron rich silicate mineral that is a member of the forsterite–fayalite series (forsterite fayalite… …   Universalium

  • fayalite — fajalitas statusas T sritis chemija apibrėžtis Mineralas. formulė Fe₂[SiO₄] atitikmenys: angl. fayalite rus. фаялит …   Chemijos terminų aiškinamasis žodynas

  • fayalite — noun Yellow, olive green, brown or black mineral with orthorhombic crystals of the olivine group, FeSiO …   Wiktionary

  • fayalite — (entrée créée par le supplément) (fa ia li t ) s. f. Péridot d un noir de fer, à éclat métallique, dont la magnésie a été remplacée presque entièrement par l oxyde ferreux, PISANI, Minéralogie, 1875 …   Dictionnaire de la Langue Française d'Émile Littré

  • fayalite — Смотри Фаялит …   Энциклопедический словарь по металлургии

  • fayalite — fa·yal·ite …   English syllables

  • fayalite — /ˈfeɪəlaɪt/ (say fayuhluyt), /faɪˈalaɪt/ (say fuy ahluyt) noun a black, greenish, or brownish mineral of the olivine group, ferrous orthosilicate, Fe2SiO4; iron olivine. {from Fayal, an island in the Azores, in the N Atlantic + ite1} …  

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