Minerals limonite

The sesqui-hydrate, 2Fe203.3H20, is generally regarded as resulting when the normal trihydrate is allowed to dry in a vacuum. It occurs in nature as the mineral limonite (see p. 18), and is a valuable source of iron. It is probably not a chemical entity but a colloidal substance containing adsorbed water.5... 

Damage to stone occurs also for the corrosion of metallic bars used for anchoring blocks of stone with each other and with the structural framework. Oxidation of iron produces the mineral limonite (FeO-OH) which has greater volume than the parent iron. This volume increment generates stresses sufficient to disintegrate the stone. The presence of SO2 and other acid components decidedly accelerates the decay phenomenon. 

Oxidation of iron produces the mineral limonite (FeO.OH) which has greater volume than the parent iron. This volume increment generates stresses sufficient to disintegrate the stone. 

The laterites can be divided into three general classifications (/) iron nickeliferrous limonite which contains approximately 0.8—1.5 wt % nickel. The nickel to cobalt ratios for these ores are typically 10 1 (2) high siUcon serpentinous ores that contain more than 1.5 wt % nickel and (J) a transition ore between type 1 and type 2 containing about 0.7—0.2 wt % nickel and a nickel to cobalt ratio of approximately 50 1. Laterites found in the United States (8) contain 0.5—1.2 wt % nickel and the nickel occurs as the mineral goethite. Cobalt occurs in the lateritic ore with manganese oxide at an estimated wt % of 0.06 to 0.25 (9). 

In the case of carbonatite ores, a beneficiation process involves preflotation followed by reactivation and flotation of pyrochlore. In the case of pegmatitic ores that contain silicates, biotite, albite and limonite, as the gangue minerals, direct flotation of pyrochlore can be achieved with a variety of different collectors. 

Flotation of pyrochlore using sodium alkyl sulphate is dependent on flotation pH. At a pH above 5.5, no pyrochlore flotation is achieved. At this pH, microcline, limonite and aegirine were floated. It appears that the use of alkyl sulphate at slightly acidic to alkaline pH number of gangue minerals can be selectively floated from pyrochlore. At a pH between 1.5 and 3.0, alkyl sulphate floats pyrochlore and zircon, whereas floatability of limonite, microline and aegirine is greatly reduced (Figure 22.4). 

Occurrence. Iron is highly abundant (about 5.5% of the earth s crust) it is believed that the core of earth is mostly molten iron together with nickel. The most common ore is haematite (Fe203). Iron is found in other minerals such as magnetite, limonite, siderite, pyrite. Iron is found native in meteorites known as siderites. 

Hersh and coworkers (16) examined electrostatic precipitator samples using petrographic microscopy. The minerals along with their chemical formula eind mode of occurrence are given in Table VIII. Kaolinite and limonite were by far the most abundant minerals detected. 

Mineralization was represented by quartz-chlorite-carbonate-sulfide veins with visible chalcopyrite, galena, sphalerite, pyrrhotite, cobaltite, limonite and malachite. Fractures filled by veins are identified on aerial photos as one submeridional zone up to 20 m thick and 500 m long. The northeastern linear system represented by a shear zone containing veinlets with arsenopyrite, bismuthine, gold and silver sulfosalts. Twelve veins that differ in extent and intensity of mineralization were discovered, with some veins yielding 3 wt. % Sn, 3 wt. % Cu, and up to 250 g/t Ag. 

Iron oxides in soils have in common that they are of extremely small crystal size and/or low crystal order. This, in combination with their low concentration (only tens g kg in most soils) explains why soil iron oxides have escaped identification for a long time in spite of their obvious existence as seen from the soil colour. In the past, therefore, Fe oxides in surface environments have been considered to be amorphous to X-rays and often called limonite , which mineralogically, is an obsolete term. Furthermore, in order to identify the clay minerals in soils properly, Fe oxides are usually removed before X-ray diffraction methods are applied (Alexander et al., 1939 Mehra Jackson, 1960). 

GANGUE. The minerals and rock mined with a metallic ore but valueless in themselves or used only as a by-product. They are separated from the ore in the milling and extraction processes, often as slag. Common gangue materials are quartz, calcite, limonite. feldspar, pyrite. etc. 

PSEUDOMORPH. In mineralogy and geology, a mineral, having the crystal form of one species and the chemical composition of another. Typical pseudomorphs are malachite in the form of cuprite, barite in the form of quartz, limonite in the form of pyrite. In such cases of pseudomorphism the evidence seems to be that there has been a complete chemical and molecular change but without any change of the original outward form. See also Mineralogy. 

Fe203, Ti02, MgO, and CaO are nearly always present in kaolinite samples and K20 and Na20 are usually present. Most samples either have excess Si02 or A1203-Mineral impurities such as quartz, anatase, rutile, pyrite, limonite, feldspar, mica, montmorillonite, and various iron and titanium oxides are commonly present in addition to a number of other minerals. Si and Al, in the form of hydroxides, apparently can occur as coatings on the kaolinite layers. Although many of these impurities are usually identified, seldom is the analysis sufficiently quantitative to determine if all the deviation from the ideal composition is due to these impurities. 

When oxidised by weathering, the final product of pyrites is hydrated ferric oxide or rust, as stated above, but the method of oxidation depends upon circumstances. In the absence of carbon dioxide or carbonates, it is usual for oxidation to ferrous sulphate to first take place whence the mineral copperas or melanterite (see below). This, in course of time, oxidises to limonite. In the presence of carbon dioxide, however, it appears that the sulphate is not first formed, but the readily oxidisable carbonate, which is then converted into limonite.3... 

In addition to a-FeOOH, (/8, y, 8)-FeOOH have been synthesized. The last varieties apparently are metastable and convert to hematite a-Fe203 when boiled, with a-FeOOH formed as an intermediate phase (Butler and Ison, 1965). All the other mineral species (limonite, turgite, hydrogoethite) are goethite with a variable amount of adsorbed water, or mixtures of goethite, amorphous iron hydroxides, and sometimes hematite. 

In contrast to the very restricted size of the soil-gas anomaly at Jabiluka, Zonghua and Yangfen (1981) describe broad anomalies associated with a buried skam Cu deposit near Shanghai, China. The ore body is confined to the contact zone of granodiorite and Palaeozoic and Mesozoic sedimentary rocks. The major sulphide minerals in the ore body are chalcopyrite, pyrite and molybdenite. Part of the deposit has been oxidised to limonite. The area is covered by 140-180 m of alluvium. A soil-gas survey of the area was complemented by a multielement study of soils including the determination of Hg. Significant anomalies of Hg in soil and soil gas occurred above the buried sulphide... 

Limonite is a rock that contains goethite, lepidocrocite, and other minerals. Its empirical formnla is Fe2O3nH2O (n > 1). PZCs/IEPs of limonites are presented in Tables 3.529 and 3.530. ... 

The appearance of polynuclear complexes sometimes facilitates polymerization and formation of large macromolecules, which are capable of making solution into colloid. For instance, at hydrolysis of oxide iron Fe may form a complex compound Fe(OH)/, which polymerizes and forms large colloid molecules [Fe(OH)j]. In such solutions precipitates mineral of iron hydroxide - the limonite. Similar colloid forms occurrence are typical of many chelate complex compounds with organic ligands. 

Chemical weathering is least effective with minerals of hypogene rocks (quartz, feldspars, micas, etc.). Their dissolution is very slow and is accompanied by the formation of secondary, even less soluble hypergene minerals (clay, gibbsite, boehmite, limonite, etc.). The rate of such substitution depends on intensity of water-exchange with the surface and aggressiveness... 

The goethite pseudomorph is an easy one—the original pyrite is in the isometric system. Incidentally, these particular pseudomorphs are sometimes referred to as limonite. The term limonite is not an accepted mineral name and is used when the composition of the iron oxide is uncertain. The names of minerals are... 

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