Limonite is an iron earth mineraloid among the first colors of the Stone Age palette. Grinding limonite produces yellow ochre. Other early pigments include red from iron ores, madder and the kermes insect. Blue of woad is found in Neolithic cave burials in France.
One of the earliest known colors, limonite is also called yellow ochre (ocher), yellow oxide or hydrated ferric oxide (rust). It's largely composed of goethite, one of the three primary iron ores. The other two are hematite and magnetite.
Ground hematite makes red pigment iron oxide, and is the primary constituent in red ocher. Magnetite yields a black pigment, today known commercially as Mars Black. The "Mars" colors are iron oxides, as planet Mars is associated with the metal iron.
The luster of limonite is described as matte and earthy. An amorphous mineraloid, limonite is opaque and leaves a yellowish streak. It can be used as a paint, color tint, dye and glaze for ceramics.
Limonite develops through erosion of different iron minerals. It's created by oxidation and hydration of iron sulfide minerals, or by chemical weathering of other minerals rich in iron, such as olivine or pyroxene. Natural weathering can uncover limonite sources.
Limonite as a broad term refers to a fine-grained aggregate, or blend of small iron oxide particles. The minerals are mainly goethite, with potential presence of hematite, lepidochrocite, and other minerals.
Limonite precipitates in groundwater, deposited on the surface. Once it hardens it's no longer soluble in water. It can be ground into pigment or powder.
Ochres are natural earth pigments of iron oxide with various quantities of clay and sand minerals. Limonite is the common constituent in all ocher colors including yellow, orange, red, browns, rarely greenish. Producing warm gold tones, it's less prominent in purple ochre.
The name limonite comes from the Ancient Greek λειμών (leimṓn), meaning "wet meadow", or λίμνη (límnē), or "marshy lake", referring to its presence as bog iron ore in meadows and marshes. In brown form, it's sometimes called brown hematite or brown iron ore.
The first primary use of limonite is as pigment. The raw yellow mineraloid produces yellow ochre, especially vibrant on the isle of Cyprus, where copper deposits also abound. The color tones of limonite vary considerably depending on the constituent minerals.
Once ground to pigment, cleaned, strained and dried, the ochers can be carried anywhere in powder form. Early artists mix the pigment with water, oil or animal fat. Yellow ocher is used through the history of art. It's one of the colors best suited for egg tempera painting.
It's favored in rendering natural landscapes, sunsets and skin tones. Limonite pigment can be mixed with other colors for a range of warm earth hues. Yellow ocher is a featured color in cave paintings and later wall paint.
As well as in art, early people use limonite and other ocher and natural pigments as personal makeup for skin, hair and fashion. Recent scientific evidence confirms ochres can diminish harmful effects of exposure to ultraviolet radiation (UVR).
Darker forms of limonite produce earthy brown tones. Roasting limonite changes it partially to hematite, producing red ochres, burnt umber and sienna hues. Roasting also relates to the magnetism of limonite, which is at its most magnetic at 700°C (1292°F).
Yellow ochre from limonite is one of the colors used by early Chinese artists. It's used in both paint and fabric dyes by the ancient Egyptians, in the frescos of Minoans and occurs in raw form in some Mesopotamian clays.
Chemically, limonite is primarily composed of iron hydroxides and other impurities, and may contain trace amounts of other elements such as aluminum, manganese, and nickel. One of its primary constituents is goethite, or brown ochre.
Limonite has a hardness of 4.5 - 5.5 on the Mohs hardness scale and can be scratched with a knife. For comparison glass is 5.5 - 6.5.
A major iron component in lateritic or highly weathered soils, limonite ores are a source of nickel, potentially cobalt and other valuable metals present as trace elements. Limonite is often deposited in run-off streams from mining operations.
Limonite is usually non-toxic but may grow together with poisonous elements such as chalcanthite, a beautiful blue crystalline copper mutation. Handling the stone is not very dangerous but ingestion can cause copper poisoning.
Evidence of ochre pigment extraction goes back to Africa in the times of archaic homo sapiens, about 300,000 years ago. Throughout history limonite has various uses in art and industry.
Pigments - used since prehistory as a pigment in artwork and beauty treatments. It's a popular material in paints, glazes, coloring and coatings, especially earthy or ochre colors. It can be used as a dye. The ochers are suited to frescos, which bind the pigment into the wall.
Soil conditioner - added to acidic soils, it neutralizes soil acidity and infuses nutrients including iron, magnesium, and calcium.
Water treatment - Use of limonite as a filter in water treatment systems removes impurities such as arsenic, lead, and other heavy metals.
Cement - as a source of iron oxide in cement production, limonite is both a coloring agent and a flux to lower the melting point of raw materials.
Research - as a common mineral in soil and sedimentary rocks, limonite can indicate past environmental conditions and events.
Limonite is found throughout the world. Today the best sites for limonite include Lorraine, Luxembourg, Sweden, Germany (Bavaria, Saxony), Austria, England, and the United States.
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