Limonite

File:Limonite bog iron cm01.jpg ore]]

Limonite is named for the Ancient Greek word {{wikt-lang|grc|λειμών}} ({{grc-transl|λειμών}} {{IPA|grc|leː.mɔ̌ːn|}}), meaning "wet meadow", or {{wikt-lang|grc|λίμνη}} ({{grc-transl|λίμνη}} {{IPA|grc|lím.nɛː|}}), meaning "marshy lake", as an allusion to its occurrence as {{em|bog iron ore}} in meadows and marshes.{{Mindat |id=2402 |name=Limonite}} In its brown form, it is sometimes called brown hematite{{cite book |editor1-last=Jackson|editor1-first=Julia A. |title=Glossary of Geology |date=1997 |publisher=American Geological Institute |location=Alexandria, Virginia |isbn=0922152349 |edition=4th |chapter=brown hematite}} or brown iron ore.{{sfn|Jackson|1997|loc="brown iron ore"}}

Limonite is relatively dense with a specific gravity varying from 2.7 to 4.3.Northrop, Stuart A. (1959) "Limonite" Minerals of New Mexico (revised edition) University of New Mexico Press, Albuquerque, New Mexico, pp. 329–333, {{OCLC|2753195}} It is usually medium to dark yellowish brown in color. The streak of limonite on an unglazed porcelain plate is always yellowish brown, a character which distinguishes it from hematite with a red streak, or from magnetite with a black streak. The hardness is quite variable, ranging from 1 to 5. In thin section it appears as red, yellow, or brown and has a high index of refraction, 2.0–2.4. Limonite minerals are strongly birefringent, but grain sizes are usually too small for this to be detectable.{{cite book |last1=Nesse |first1=William D. |title=Introduction to mineralogy |date=2000 |publisher=Oxford University Press |location=New York |isbn=9780195106916 |pages=371–372}}

Although originally defined as a single mineral, limonite is now recognized as a field term for a mixture of related hydrated iron oxide minerals,{{cite book |last1=Klein |first1=Cornelis |last2=Hurlbut |first2=Cornelius S. Jr. |title=Manual of mineralogy : (after James D. Dana) |date=1993 |publisher=Wiley |location=New York |isbn=047157452X |edition=21st}} among them goethite, lepidocrocite, akaganeite,{{cite journal |last1=Mackay |first1=A. L. |title=β-Ferric oxyhydroxide—akaganéite |journal=Mineralogical Magazine and Journal of the Mineralogical Society |date=December 1962 |volume=33 |issue=259 |pages=270–280 |doi=10.1180/minmag.1962.033.259.02|bibcode=1962MinM...33..270M }} and jarosite.{{cite journal |last1=Zuo |first1=Pengfei |last2=Sun |first2=Jiangtao |last3=Liu |first3=Xuefei |last4=Hao |first4=Jinhua |last5=Zheng |first5=Deshun |last6=Li |first6=Yu |title=Two types of jarosite in the early Cambrian sedimentary rocks: Insights for genesis and transformation of jarosite on Mars |journal=Icarus |date=November 2021 |volume=369 |pages=114651 |doi=10.1016/j.icarus.2021.114651|bibcode=2021Icar..36914651Z }} Determination of the precise mineral composition is practical only with X-ray diffraction techniques. Individual minerals in limonite may form crystals, but limonite does not, although specimens may show a fibrous or microcrystalline structure,Boswell, P. F. and Blanchard, Roland (1929) "Cellular structure in limonite" Economic Geology 24(8): pp. 791–796 and limonite often occurs in concretionary forms or in compact and earthy masses; sometimes mammillary, botryoidal, reniform or stalactitic. Because of its amorphous nature, and occurrence in hydrated areas limonite often presents as a clay or mudstone. However, there are limonite pseudomorphs after other minerals such as pyrite. This means that chemical weathering transforms the crystals of pyrite into limonite by hydrating the molecules, but the external shape of the pyrite crystal remains. Limonite pseudomorphs have also been formed from other iron oxides, hematite and magnetite; from the carbonate siderite and from iron rich silicates such as almandine garnets.

File:La Palma Limonit.jpg|Limonite deposited from mine runoff

File:Galena Limonite.jpg|Galena and limonite

File:GranadaEZ.jpg|Limonite pseudomorphs after garnet

Limonite usually forms from the hydration of hematite and magnetite, from the oxidation and hydration of iron rich sulfide minerals, and chemical weathering of other iron rich minerals such as olivine, pyroxene, amphibole, and biotite. It is often the major iron component in lateritic soils, and limonite laterite ores are a source of nickel and potentially cobalt and other valuable metals, present as trace elements.{{cite journal |last1=Rubisov |first1=D.H |last2=Krowinkel |first2=J.M |last3=Papangelakis |first3=V.G |title=Sulphuric acid pressure leaching of laterites — universal kinetics of nickel dissolution for limonites and limonitic/saprolitic blends |journal=Hydrometallurgy |date=November 2000 |volume=58 |issue=1 |pages=1–11 |doi=10.1016/S0304-386X(00)00094-3}}{{cite journal |last1=Gao |first1=Jian-ming |last2=Cheng |first2=Fangqin |title=Study on the preparation of spinel ferrites with enhanced magnetic properties using limonite laterite ore as raw materials |journal=Journal of Magnetism and Magnetic Materials |date=August 2018 |volume=460 |pages=213–222 |doi=10.1016/j.jmmm.2018.04.010|bibcode=2018JMMM..460..213G |s2cid=125368631 }} It is often deposited in run-off streams from mining operations.

File:Limonite concretion.jpg of a uranium mine]]

Nickel-rich limonite ores represent the largest reserves of nickel. Such minerals are classified as lateritic nickel ore deposits.{{Ullmann|author=Kerfoot, Derek G. E. |title=Nickel|doi=10.1002/14356007.a17_157|year=2005}}

One of the first uses was as a pigment. The yellow form produced yellow ochre for which Cyprus was famous,Constantinou, G. and Govett, G. J. S. (1972). "Genesis of sulphide deposits, ochre and umber of Cyprus". Transactions of the Institution of Mining and Metallurgy. 81: pp. 34–46 while the darker forms produced more earthy tones. Roasting the limonite changed it partially to hematite, producing red ochres, burnt umbers and siennas.Heckel, George B. (1910) "Iron Oxide Paints". Paint, oil and drug review. 50(4): pp. 14–21, [https://books.google.com/books?id=7P9YAAAAYAAJ&pg=PA52 page 14] Bog iron ore and limonite mudstones are mined as a source of iron.

Iron caps or gossans of siliceous iron oxide typically form as the result of intensive oxidation of sulfide ore deposits.Brown, G. Chester (1915) Mines and mineral resources of Shasta county, Siskiyou county, Trinity county California State Mining Bureau, California State Printing Office, Sacramento, California, [https://books.google.com/books?id=WbpIAAAAMAAJ&pg=PA15 pages 15–16], {{OCLC|5458708}} These gossans were used by prospectors as guides to buried ore.

Limonite was mined for its ancillary gold content. The oxidation of sulfide deposits which contained gold, often resulted in the concentration of gold in the iron oxide and quartz of the gossans. 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.

{{main|History of ferrous metallurgy}}{{See|Ochre#History}}

Limonite was one of the earliest materials used as a pigment by humans, and can be seen in Neolithic cave paintings and pictographs.Wilford, John Noble (13 October 2011) [https://www.nytimes.com/2011/10/14/science/14paint.html?_r=2&hp "In African Cave, Signs of an Ancient Paint Factory"] The New York Times; hardcopy published 14 October 2011 under title "African Cave, Ancient Paint Factory Pushes Human Symbolic Thought ‘Far Back’" New York edition page A-14; archived by WebCite [https://web.archive.org/web/20120103231857/http://www.nytimes.com/2011/10/14/science/14paint.html?_r=1 page 1] and [https://web.archive.org/web/20220617104805/https://www.nytimes.com/2011/10/14/science/14paint.html?_r=3&pagewanted=2 page 2] on 11 March 2012

While the first iron ore was likely meteoric iron, and hematite was far easier to smelt, in Africa, where the first evidence of iron metallurgy occurs,{{dubious|date=April 2022|Ferrous metallurgy in Africa}} limonite is the most prevalent iron ore. Before smelting, as the ore was heated and the water driven off, more and more of the limonite was converted to hematite. The ore was then pounded as it was heated above 1250 °C,Iron oxide becomes metallic iron at roughly 1250°C, almost 300 degrees below iron's melting point of 1538°C. at which temperature the metallic iron begins sticking together and non-metallic impurities are thrown off as sparks.{{dubious|date=April 2022|Ferrous metallurgy in Africa}} Complex systems developed, notably in Tanzania, to process limonite.Schmidt, Peter and Avery, Donald H. (22 September 1978) [http://www.sciencemag.org/cgi/content/abstract/201/4361/1085 "Complex Iron Smelting and Prehistoric Culture in Tanzania"] Science201(4361): pp. 1085–1089 Nonetheless, hematite and magnetite remained the ores of choice when smelting was by bloomeries, and it was only with the development of blast furnaces in the 1st century BCE in ChinaWagner, Donald B. (1999) [http://www.staff.hum.ku.dk/dbwagner/EARFE/EARFE.html "The earliest use of iron in China"] {{webarchive|url=https://web.archive.org/web/20060718053841/http://www.staff.hum.ku.dk/dbwagner/EARFE/EARFE.html |date=2006-07-18 }} pp. 1–9 In Young, Suzanne M. M. et al. (editors) (1999) Metals in Antiquity Archaeopress, Oxford, England, {{ISBN|978-1-84171-008-2}} and about 1150 CE in Europe,Jockenhövel, Albrecht et al. (1997) [https://www.uni-muenster.de/UrFruehGeschichte/forschen/maerkischessauerland_engl.html "Archaeological Investigations on the Beginning of Blast Furnace-Technology in Central Europe"] Abteilung für Ur- und Frühgeschichtliche Archäologie, Westfälische Wilhelms-Universität Münster; abstract published as: Jockenhövel, A. (1997) "Archaeological Investigations on the Beginning of Blast Furnace-Technology in Central Europe". In Crew, Peter and Crew, Susan (editors) (1997) Early Ironworking in Europe: Archaeology and Experiment: Abstracts of the International Conference at Plas Tan y Bwlch 19–25 Sept. 1997 (Plas Tan y Bwlch Occasional Papers No 3) Snowdonia National Park Study Centre, Gwynedd, Wales, pp. 56–58. {{OCLC|470699473}}. Archived [https://web.archive.org/web/20130224111115/http://www.uni-muenster.de/UrFruehGeschichte/forschen/maerkischessauerland_engl.html here] by WebCite on 11 March 2012 that the brown iron ore of limonite could be used to best advantage.

Bog iron ore and limonite were mined in the US, but this ended with the development of advanced mining techniques.

Goldbearing 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.

As saprolite deposits have been exhausted in many mining sites, limonite has become the most prominent source of nickel for use in energy dense batteries.

• Ore genesis

{{Reflist}}

{{Commons|Limonite}}

• [https://web.archive.org/web/20050622082227/http://mineral.galleries.com/minerals/oxides/limonite/limonite.htm Mineral galleries]
• [http://www.mindat.org/min-2402.html Mindat]
• [https://web.archive.org/web/20100926205333/http://minelinks.com/alluvial/deposits5.html Gold and limonite]

Category:Iron ores

Category:Rocks