Limonite

Julian Herbert

Physical Properties

  • It varies in color from a bright lemony yellow to a drab grayish brown.
  • The streak of limonite on an unglazed porcelain plate is always brownish, a character which distinguishes it from hematite with a red streak or from magnetite with a black streak.
  • The hardness is variable, but generally in the 4 - 5.5 range.

Chemical Properties

  • Formula:

    FeO(OH) · nH2O


  • Limonite is not a true mineral but a mixture of similar hydrated iron oxide minerals.
  • Limonite forms mostly in or near oxidized iron and other metal ore deposits, and as sedimentary beds.
  • Limonite has been known to pseudomorph other minerals such aspyrite, meaning it replaces a crystal of pyrite with limonite but keeps the shape of the pyrite crystal.

Acquisition/Mining

  • A very common material in the oxidized zones of iron-bearing deposits, it is produced by the decomposition of many iron minerals, particularly pyrite, with water being retained in varying amounts.
  • In Africa, where the first evidence of iron metallurgy occurs, 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, at which temperature the metallic iron begins sticking together and non-metallic impurities are thrown off as sparks.
  • Smelting is a form of extractive metallurgy. Smelting uses heat and a chemical reducing agent to decompose the ore.

Limonite Processing

  • During mining, barren rocks mix in to make ore dilution. For this ore, adopt crush but don't grind, under this circumstance of coarse granularity, by gravity separation, discard coarse grain tailings, to recover geology grade and obtain medium grade concentrate in coarse grains, or further process, or directly send into blast-furnace process, this is named as coarse gravity separation; another is that fine disseminated red ore or mixed ore(that contain weak magnetic red ore and strong magnetic magnetite), through crushing and grinding, iron minerals are separated, and through gravity separation or magnetic reconnection separation, get fine and high grade concentrate, this is called fine-grained hematite gravity separation.

Limonite Marketing: Wulfenite on Limonite

  • $9,500.00
  • Red Cloud Mine, La Paz County, Arizona, USA
  • Once in the notable collection of Steve Smale and photographed in the Mineralogical Record in the early 1990's, this wulfenite specimen features crystals that are lustrous and translucent and bright orange in color, aesthetically perched on an ocherous matrix. The largest crystal measures 2 cm across on what is considered a competition-quality miniature. This was from the small "Barlow Pocket" discovery in 1996 by Bruce Barlow and associates. The color and quality of this specimen approaches those from the famous Ed Over pocket in 1938, the only find here to do so in the last 80 years! Only a handful of specimens were found, of which this is certainly among the best. It is elegant, by any meaning of that word! It shines with the top luster, and is dramatic from either side. Illustrated in a short article on this remarkable one-pocket find in Mineralogical Record.
  • This is just one instance of something with limonite being sold. Prices vary from $60-$9,500.
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Limonite Uses

  • One of the first uses was as a pigment.
  • The yellow form produced yellow ochre for which Cyprus was famous, while the darker forms produced more earthy tones.
  • Roasting the limonite changed it partially to hematite, producing red ochres, burnt umbers and siennas.

  • Limonite mudstones are mined as a source of iron, although commercial mining of them has ceased in the United States.

Environmental Impacts & Solutions

  • Limonite has to be concentrated before extracted and purified. This often results in lots of waste material that must be dealt with from an environment of view.
  • Dust from mining–quarrying or processing can be reduced by air filter and precipitation systems and even hosing water on dusty areas or spoil heaps or carried away to somewhere else via tall chimneys.

  • Scarring of the landscape from mining, quarrying, waste tips etc. as well as loss of wildlife habitat.


  • Pollution can be reduced by cleaning the 'waste' or 'used' air, water and waste gases etc. of toxic or acidic materials e.g.
  • Sulphur dioxide gas from copper extraction of its sulphide ore is an irritating poisonous gas which can also cause acid rain, but it can be converted to the useful, therefore salable industrial chemical concentrated sulphuric acid.
  • Acidic gases like sulphur dioxide can be removed by bubbling through an alkali solution such as calcium hydroxide solution where it is neutralised and oxidised to harmless calcium sulphate. Cleaning a gas in this way is called gas scrubbing.

Works Cited