How much iron is in Limonite?

Matte or has a metallic, silky, resinous sheen. Hardness 1,5-5,5; variable: there are soft, medium-hard and hard varieties. Specific gravity: 3,3-3,9 g/cm₃. Color brown, ocher-yellow, black. The line is rusty-brown, ocher-yellow. There is no cleavage. Solid, dense, sintered; nodules, geodes, oolites, called bean and bog ore; sometimes earthy (turf ores), powdery; in addition, uncemented oolites. Amorphous; sometimes there are crystals in the form of cubes, pentagonal dodecahedrons – the result of chemical weathering of pyrite (pseudomorphoses of pyrite) or false forms of siderite and organic remains.

Features. The color of limonite is rusty-brown, ocher-yellow, black; the streak is rusty-brown, ocher-yellow. Brown iron ore has much in common with bauxite in appearance. It differs in color (bauxite’s color is brick-red, brown-red, pink), line (bauxite’s line is paler) and density (bauxite is lighter than brown iron ore).

Chemical properties. Easily dissolves in hydrochloric acid.

Varieties:

1. Brown glass head – sintered forms with a smooth shiny surface.
2. Yellow ocher (iron ocher) – earthy, powdery limonite of ocher-yellow color. Soft.

Limonite Brown glass head. Photo by Rob Lavinsky Yellow ochre. Photo by Rob Lavinsky

Origin

Limonite is formed as a result of chemical weathering of iron-containing minerals: siderite, pyrite, chalcopyrite, hematite, magnetite, etc. Limonite is also formed as a result of the deposition of aqueous iron compounds at the bottom of swamps (swamp ore), lakes (lake ore) and in the shallow part of sea basins. This process is believed to involve iron bacteria.

Deposition of brown iron ore is also observed at the outlets of ferruginous springs. Limonite, falling into the deep zones of the Earth, under conditions of high temperature and pressure, loses water and turns into hematite and magnetite.

Satellites. Siderite, pyrolusite. Minerals, as a result of the chemical change of which brown iron ore is formed: siderite, pyrite, chalcopyrite, hematite, serpentine, hornblende, augite, biotite, ferruginous chlorites.

Application

Limonite serves as an ore for iron production. Powdery, earthy limonite is used as a paint (ochre, umber).

Limonite deposits

There are numerous deposits of limonite in Russia. Large reserves of brown iron ore have been explored in the West Siberian iron ore basin, constituting a significant part of all world reserves of iron ore (in the east of Western Siberia there is one of the world’s largest iron ore basins containing brown iron ore – the richest Bakcharskoe deposit is located northwest of Tomsk, the largest Kolpashevskoye deposit is in the Tomsk region). The Orsko-Khalilovskoye deposit (Southern Urals) arose as a result of chemical weathering of ultramafic igneous rocks. Limonite from the Alapaevsky and Bakalsky deposits (Middle Urals) was formed in the upper part of siderite (iron hat) as a result of chemical weathering of the latter. Brown iron ore of the Kyshtym and Karabash deposits (Ural) appeared as a result of chemical weathering of pyrite and other sulfides in the upper part of the deposits – limonite represents their “iron hat”. The deposits of the Lipetsk and Tula regions are lake and swamp deposits of Late Paleozoic age. In Karelia, limonite occurs at the bottom of modern lakes. After 10-15 years, the depleted reserves are restored again. Finally, the Komarovo-Zigazinskoye field (Bashkortostan) should be noted. Deposits of minium, umber and ocher are found in the Kursk magnetic anomaly.

Large iron ore regions are located in Kazakhstan – the Kustanai and Aral iron ore regions. The world’s largest deposit of brown iron ore is located in the Kostanay region.

The Kerch field is located in the northern and eastern outskirts of the Kerch Peninsula (Ukraine). Limonite deposits on the Taman Peninsula are similar to those on the Kerch Peninsula.

Industrial deposits of ocher and mummies are available in Tajikistan (near Yantak), golden-yellow ocher is mined in the Dzhangeldinskoye deposit (Kyzylkum).

The most significant iron ore deposits in Western Europe are represented by brown oolitic iron ore of sedimentary origin (Lorraine, Luxembourg).

Limonite is an iron ore consisting of a mixture of hydrated iron (III) oxide-hydroxides in various compositions. The general formula is often written as FeO(OH) nH₂O, although this is not entirely accurate since the ratio of oxide to hydroxide can vary quite widely. Limonite is one of the two main iron ores (the other is hematite) and has been mined for iron since at least 2500 BC.

Titles

The name “limonite” comes from the Greek word for “meadow” (λειμών), which refers to its distribution as bog iron ore in meadows and swamps (a footnote should be added here, as there is a possibility that the name comes from the Latin “limus”, which means “dirt”, or from its lemon-yellow color). In its brown form, it is sometimes called brown hematite or brown iron ore, and in its bright yellow form, lemon rock or yellow iron ore.

Features

Limonite is relatively dense, with a specific gravity of 2,7 to 4,3. Color varies from bright lemon yellow to dull grayish brown. A limonite stripe on an unglazed porcelain plate is always brownish, a feature that distinguishes it from red-banded hematite or black-banded magnetite. Hardness is variable, but typically in the range of 4–5,5.

Although originally identified as a single mineral, limonite is now recognized as a mixture of related hydrated iron oxide minerals, including goethite, akaganeite, lepidocrocite, and jarosite. Individual minerals in limonite may form crystals that limonite does not have, although specimens may have a fibrous or microcrystalline structure, and limonite often occurs in nodular forms or in compressed and earthy masses; sometimes in mamillary, botryoidal, reniform or stalactitic. Because of its amorphous nature and occurrence in hydrated areas, limonite is often clay or mudstone. However, limonite pseudomorphs exist after other minerals such as pyrite. This means that chemical weathering turns the pyrite crystals into limonite by hydrating the molecules, but the outer shape of the pyrite crystal remains. Pseudomorphs of limonite are also formed from other iron oxides, hematite and magnetite; from carbonate siderite and from iron-rich silicates such as almandine garnets.

Formation

Limonite typically forms from the hydration of hematite and magnetite, from the oxidation and hydration of iron-rich sulfide minerals, and the chemical weathering of other iron-rich minerals such as olivine, pyroxene, amphibole, and biotite. It is often the main component of iron in lateritic soils. Often deposited in runoff from mining operations.

Uses of limonite

One of the first uses was as a pigment. The yellow mold produced the yellow ocher for which Cyprus was famous, and the darker molds produced an earthier paint. Firing limonite partially changes it to hematite, allowing the production of red ochres, burnt umbers and siennas.

Bog iron ore and limonite mudstones are mined as a source of iron, although commercial mining has ceased in some countries (such as the United States).

Intense oxidation of sulfide ore deposits typically results in the formation of iron hats, or gossan, of siliceous iron oxide. These gossan were used by prospectors as guides to buried ore. In addition, oxidation of those sulfide deposits that contained gold often results in gold concentrations in iron oxide and gossan quartz. Gold-bearing limonite gossan rocks are mined in Shasta County, California. Similar deposits are being developed near the Rio Tinto (“red river”) in Spain and Mount Morgan in Australia. In the Dahlonega Gold Belt in Lumpkin County, Georgia, gold is mined from limonite-rich laterite or saprolite soil. The gold of the primary veins is concentrated in limonites of deeply weathered rocks. Another typical example is the deeply weathered iron formations of Brazil, due to which the soils are enriched with gold and limonite.

History

While the first iron ore was probably meteoric iron and hematite was much easier to smelt, in Africa, known for the first evidence of iron metallurgy, limonite is the most common iron ore. Before smelting, as the ore was heated and the water was removed, more and more limonite was converted to hematite. The ore was then crushed when it was heated above 1250°C, the temperature at which the iron begins to clump together and non-metallic impurities are thrown off as sparks. Sophisticated systems have been developed for processing limonite, especially in Tanzania. However, hematite and magnetite remained the ores of choice when smelting was done using cheese furnaces, and only with the development of blast furnaces in 1150st century BC China and around XNUMX AD. In Europe, it became possible to use the brown iron ore limonite to the greatest benefit.

Regarding the use of limonite as a pigment, it was one of the earliest materials used by man and can be seen in Neolithic caves in paintings and pictographs.