Limonite


Limonite

Limonite is an ore consisting in a mixture of hydrated iron(III) oxide-hydroxide of varying composition. The generic formula is frequently written as FeO(OH)·nH2O, although this is not entirely accurate as limonite often contains a varying amount of oxide compared to hydroxide.

Together with hematite, it has been mined as ore for the production of iron. Limonite is heavy and yellowish-brown. It is a very common amorphous substance though can be tricky to find when mined with hematite and bog ore.

It is not a true mineral and it is composed by a mixture of similar hydrated iron oxide minerals, mostly goethite with lepidocrocite, jarosite, and others. Limonite forms mostly in or near oxidized iron and other metal ore deposits and as sedimentary beds. Limonite may occur as the cementing material in iron rich sandstones. Also known as the Lemon Rock.

It is never crystallized into macroscopic crystals, but may have a fibrous or microcrystalline structure, and commonly occurs in concretionary forms or in compact and earthy masses; sometimes mammillary, botryoidal, reniform or stalactitic. The colour presents various shades of brown and yellow, and the streak is always brownish, a character which distinguishes it from hematite with a red, or from magnetite with a black streak. It is sometimes called brown hematite or brown iron ore.

Limonite has been known to form pseudomorphs after other minerals such as pyrite, meaning that the chemical weathering transforms the crystal of pyrite into limonite but keeps the external shape of the pyrite crystal. It has also been formed from other iron oxides, hematite and magnetite; the carbonate siderite and iron rich silicates like some garnets.

It is named from the Greek word for meadow (λειμών), in allusion to its occurrence as "bog-ore" in meadows and marshes.

The hardness is variable, but generally in the 4 - 5.5 range. The specific gravity varies from 2.9 to 4.3.

Uses of limonite

In the past bog ore or brown iron ore were mined as a source of iron. "Iron caps" or gossans of siliceous iron oxide typically forms as the result of intensive oxidation of sulfide ore deposits. These gossans were used by prospectors as guides to buried ore. In addition the oxidation of sulfide deposits which contained gold mineralization often resulted in the concentration of gold in the iron oxide and quartz of the gossans.

Gold bearing limonite gossans were productively mined in the Shasta County, California mining district. Similar deposits were mined near Rio Tinto in Spain and Mount Morgan in Australia. In the Dahlonega gold belt in Lumpkin County, Georgia gold was mined from limonite rich lateritic or saprolite soil. The gold of the primary veins was concentrated into the limonites of the deeply weathered rocks. In another example the deeply weathered iron formations of Brazil served to concentrate gold with the limonite of the resulting soils.

Limonite from occurrences with consistent color is used as the yellow-brown natural "earth" pigment "ochre".

ee also

* Bog iron
* Iron ore
* Ore genesis

External links

* [http://www.ironminers.com Abandoned Mine Research & History] .
* [http://mineral.galleries.com/minerals/oxides/limonite/limonite.htm Mineral galleries]
* [http://www.mindat.org/min-2402.html Mindat]
* [http://www.minelinks.com/alluvial/deposits5.html Gold and limonite]


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Look at other dictionaries:

  • limonite — [ limɔnit ] n. f. • 1842; de 1. limon ♦ Minér. Hydroxyde naturel de fer, brun, opaque, présent dans les minerais d hématite. ● limonite nom féminin (de limon 1) Minerai de fer, qui est un oxyde ferrique hydraté naturel d aspect le plus souvent… …   Encyclopédie Universelle

  • Limonite — Chapea …   Wikipédia en Français

  • Limonite — Li mon*ite (l[imac] m[o^]n*[imac]t), n. [Gr. leimw n any moist grassy place, a meadow: cf. F. limonite, G. limonit.] (Min.) Hydrous sesquioxide of iron, an important ore of iron, occurring in stalactitic, mammillary, or earthy forms, of a dark… …   The Collaborative International Dictionary of English

  • limonite — s. f. Óxido de ferro hidratado, de cor castanha amarelada.   ♦ Grafia no Brasil: limonita …   Dicionário da Língua Portuguesa

  • limonite — [lī′mə nīt΄] n. [< Gr leimōn, meadow, orig., low ground (for IE base see LIMB1) + ITE1] a brownish, amorphous mineral mixture of several iron oxides, esp. goethite, used as a coloring agent: sometimes an ore of iron: cf. YELLOW OCHER limonitic …   English World dictionary

  • limonite — limonitic /luy meuh nit ik/, adj. /luy meuh nuyt /, n. Mineral. an amorphous hydrated ferric oxide, varying in color from dark brown to yellow, used as an ore of iron. [1815 25; < Gk leimón meadow + ITE1] * * * One of the major iron minerals, a… …   Universalium

  • limonite — (li mo ni t ) s. f. 1°   Terme de minéralogie. Sorte de minerai de fer, appelé par Haüy fer oxydé géodique, et dit aussi aétite.    Limonite oolithique, variété de limonite. 2°   Terme de géologie. Couche de limon …   Dictionnaire de la Langue Française d'Émile Littré

  • limonite — li·mo·nì·te s.f. TS mineral. miscela di minerali microcristallini dati da ossidi di ferro idrati, di colore variabile da bruno a giallo e aspetto terroso {{line}} {{/line}} DATA: 1839. ETIMO: dal fr. limonite, der. di limon melma …   Dizionario italiano

  • limonite — limonitas statusas T sritis chemija apibrėžtis Mineralas. formulė FeO(OH)·nH₂O atitikmenys: angl. bod are; iron are; limonite rus. бурый железняк; гидрогетит; лимонит; озерная руда …   Chemijos terminų aiškinamasis žodynas

  • limonite — noun Etymology: German Limonit, from Greek leimōn wet meadow; akin to Greek limnē pool Date: 1823 a native hydrous ferric oxide of variable composition that is an ore of iron • limonitic adjective …   New Collegiate Dictionary


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