Goethite color

Iron Oxide Yellows. From a chemical point of view, synthetic iron oxide yellows, also known as iron gelbs, are based on the iron(III) oxide—hydroxide, a-FeO(OH), known as goethite. Color varies from light yellows to dark buffs and is primarily determined by particle size, which is usually between 0.1 and 0.8 p.m. Because of their resistance to alkahes, these are used by the building industry to color cement. Thermally, iron oxide yellows are stable up to 177°C above this temperature they dehydrate to iron(III) oxide ... 

Fig. 8.31 Left) In the Mossbauer spectrum taken in the Columbia Hills at a rock called Clovis the mineral goethite (GT) (a-FeOOH) could be identified. GT is a clear mineralogical evidence for aqueous processes on Mars. Right) The rock Clovis is made out of rather soft material as indicated by the electric drill-current when drilling the - - I cm deep hole seen in the picture. Drill fines are of brownish color. The pattern to the right of the drill hole was made by bmshing the dust off the surface by using the RAT...

Judd, D.B. Wyszecki, G. (1975) Color in business, science and industry. J. Wiley, New York Jurinak, J.J. (1964) Interaction of water with iron and titanium oxide surfaces Goethite, hematite, and anatase. J. Colloid Sci. 19 477-487... 

D.G. (1986) Relationship among derivative spectroscopy, color, crystallite dimensions and A1 substitution of synthetic goethites and hematites. Clays Clay Min. 34 625-634 Kosowski, B.M. (1993) Nanometer sized iron oxide. Paper presented at Iron oxides in colorant and chemical application". Intertec Conferences. Washington, D.C. 

Scheinost, A.C. Schulze, D.G. Schwertmann, U. (1999) Diffuse reflectance spectra of A1 substituted goethite a ligand field approach. Clays Clay Miner. 47 156-164 Scheinost, A.C. Schwertmann, U. (1999) Color identification of iron oxides and hydroxysul-fates Use and limitations. Soil Sci. Soc. Am. 

Torrent, J. Schwertmann, U. (1987) Influence of hematite on the color of red beds. J. Sediment. Petrology 57 682-686 Torrent, J. (1987) Rapid and slow phosphate sorption by Mediterranean soils effect of iron oxides. Soil Sci. Soc. Am. J. 51 78-82 Torrent, J. (1991) Activation energy of the slow reaction between phosphate and goethites of different morphology. Aust. J. Soil Res. 29 69-74... 

Goethite is the colored component of yellow ocher a weathering product mainly of siderite, sulfidic ores, and feldspar. It occurs in workable amounts mainly in the Republic of South Africa and France. The Fe2Oa content gives an indication of the iron oxide hydroxide content of the ocher, and is ca. 20% in the French deposits and ca. 55% in the South African. 

The chamosites in individual sedimentary iron formations vary widely in color which indicates there is considerable local variation in chemical composition. The sedimentary chamosites are usually quite impure, frequently containing siderite and goethite. It is necessary to make a number of assumptions in recasting analyses of these samples. 

The content and type of iron oxide affects soil chemistry. Several workers (e.g., Scheinost and Schwertmann 1995) have shown that phosphate adsorption maxima increase from red (hematitic) to yellow (goethite-rich) soils. Consequently, because yellow soils in some regions are closely correlated to soil P sorption, soil color has been used to predict the likely need for phosphate applications. 

Some simple oxides are brighdy or strongly colored, and have been used as pigments. This includes the common oxides of iron, hematite, which is red and black, and goethite (syn. limonite), which is yellow or brown. These compounds have also been called ocher, yellow ocher, or brown ocher. Minium and massicot... 

The colors of iron oxides are eaused by at least two of these electron transitions (1 and 2) as illustrated for the speetmm of goethite (Fig. 3-1). 

Fig. 3-6. Munsell colors of hematite, ferrihydrite, lepidocrocite, and goethite samples. (Figure provided by Munsell, a division of GretagMacbeth, LLC.)...

Purple hematite. Hematite crystals several j,m in size have a purple color. Such crystals can be produced by holding ferrihydrite under very strongly alkaline condition (5 M NaOH) at 70 °C for 8 days. The crystals are idiomorpliic. Some goethite is usually associated with the hematite. 

Once the syntheses are underway, the lecture can be presented. The graphs for this section as well as the list of oxides in the introduction should be available for presentation as slides or overheads. It is worth using colors for the different Fe oxides and these should be mnemonic and of course, the same on all graphs, namely, black for magnetite, red for hematite, brown for ferrihydrite, yellow for goethite and orange for lepidocrocite (Schwertmann, 1993). 

Subsequent studies reported by Sanchez del Rio et al. (2004, 2005) did not find either iron in metallic form or goethite in archeological MB. In the most recent literature, it is commonly accepted that MB coloration is mainly due to batochromic shift of the indigo absorption bands as a result of the association of the dye to the inorganic support (Reinen et al., 2004). 

The hydrated form of iron oxide, FeO(OH), limonite or goethite, can similarly be shiny black as a coarsely crystalline material but is brownish yellow when finely powdered and is responsible for the color of yellow ochre as a pure material or in a clay matrix. 

FeOOH Lepidocrocite eep Uncommon except in wet soils. Color similar to goethite. 

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