Manganese Mineral

Hundreds of manganese minerals are known. Pyrolusite MnOj is essential. Two others, manganite MnO(OH) and hausmannite Mn O, are hkewise important, while rhodochrosite MnCOj and braunite 3Mnj03 MnSiOj are of less importance, see Table 27.2. 

Mineral Formula Crystal system Color Streak color (rubbing on a porcelain surface) 

Hausmannite MnjO Tetragonal Brownish-black Reddish-brown to brown 

Rhodochrosite MnCO, Rhombohedral Rose-red or pink to gray White 

Braunite SMnjOj-MnSiO, Tetragonal Black, gray Black 

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Manganese minerals are widely distributed oxides, silicates, and carbonates are the most common. The discovery of large quantities of manganese nodules on the floor of the oceans may become a source of manganese. These nodules contain about 24% manganese together with many other elements in lesser abundance. 

Most manganese today is obtained from ores found in Russia, Brazil, Australia, Republic of S. Africa, Gabon, and India. Pyrolusite and rhodochrosite are among the most common manganese minerals. The metal is obtained by reduction of the oxide with sodium, magnesium, aluminum, or by elctrolysis. 

Pyrolusite is a black, opaque mineral with a metallic luster and is frequendy soft enough to soil the fingers. Most varieties contain several percent water. Pyrolusite is usually a secondary mineral formed by the oxidation of other manganese minerals. Romanechite, a newer name for what was once known as psilomelane [12322-95-1] (now a group name) (7), is an oxide of variable composition, usually containing several percent water. It is a hard, black amorphous material with a dull luster and commonly found ia the massive form. When free of other oxide minerals, romanechite can be identified readily by its superior hardness and lack of crystallinity. 

None of the natural sulfides of manganese are of any commercial importance. Some siUcates have been mined. Rhodonite and braunite are of iaterest because these are frequendy associated with the oxide and carbonate minerals. The chemical composition of some common manganese minerals are given ia Table 3. 

There are approximately 250 known manganese minerals. The primary ores which typically have a Mn content >35%, usually occur as oxides or hydrated oxides, or to a lesser extent as siUcates or carbonates. Table 5 Hsts the manganese-containing minerals of economic significance (10). Battery-grade manganese dioxide ores are composed predominately of nsutite, cryptomelane, and todorokite. 

Fig. 6. Thin section of Leptothrix sp. which is precipitating manganese oxide on its outermost structure called a sheath (McLean et al. 2002). The arrows point to the manganese mineral phase identified by EDS. Scale bar = 150 nm. 

Lind, C. J. and J. D. Hem, 1993, Manganese minerals and associated fine particulates in the streambed of Pinal Creek, Arizona, U.S.A., a mining-related acid drainage problem. Applied Geochemistry 8, 67-80. 

The present method is still in its early stage of application. Both ex situ and in situ type measurements are applicable to a variety of mineral/aqueous solution interfaces. For example, the mechanism of selective adsorption of cobaltous ions on manganese minerals can be studied by this method. In addition to the two Mossbauer source nuclides described in the present article, there are a number of other nuclides which can be studied. We have recently started a series of experiments using Gd-151 which is a source nuclide of Eu-151 Mossbauer spectroscopy. Development of theory on surface magnetism, especially one including relaxation is desirable. Such a theory would facilitate the interpretation of the experimental results. 

Table 18.2 Manganese Minerals in Marine Mn Nodules and Crusts. ... 

Its concentration in the earth s crust is estimated to he 0.095%. Its average concentration in seawater is 2p,g/L. Manganese also is found in large quantities in deep-sea nodules over the ocean floor at depths of 2.5 to 4 miles. The composition of some common manganese minerals is tabulated helow ... 

Under powerful laser excitation with A = 532 nm manganese minerals, such as rhodonite and rhodochrosite, exhibit orange-red Ivuninescence even at room temperature. In rhodonite it is a band peaking at 620 nm with a halfwidth of 85-95 nm and a very long decay time of 5-6 ms (Fig. 4.67c,d). Such luminescence is typical for impurity Mn ". In rhodochrosite luminescence is more complicated. The luminescence band has a maximum near 640 nm and a half-width of 80 - 90 nm, which is typical for impurity Mn ", but a decay time of only 5-lOps is very short for such a center and indicates strong energy migration (Fig. 4.67a,b). 

Taylor, R. M., and McKenzie, R. M. (1966). The association of trace elements with manganese minerals in Australian soils. Aust. J. Soil Res. 4, 29-39. 

Crane, S. E. (1981) Structural Chemistry of the Marine Manganese Minerals. Ph.D. thesis, Univ. California, San Diego. 

Keester, K. L. White, W. B. (1968) Crystal field spectra and chemical bonding in manganese minerals. In Intern. Mineral. Assoc., Pap. Proc. 5th General Meet., Cambridge, 1966. (P. Gay, A. F. Seager, H. F. W. Taylor J. Zussman, eds Mineral. Soc., London), pp. 22-35. 

Liu, R., and H. Tang. 2002. Surface acid-base characteristics of natural manganese mineral particles. Coll. Surf. A, 197 47-54. 

Mandernack, K.W., Post, J., and Tebo, B.M., Manganese mineral formation by bacterial spores of the marine Bacillus, strain SG-1 Evidence for the direct oxidation of Mn(II) to Mn(IV), Geochim. Cosmochim. Acta, 59, 4393, 1995. 

McKenzie, R.M., The synthesis of birnessite, cryptomelane, and some other oxides and hydroxides of manganese, Miner. Mag., 38, 493, 1971. 

There is a lot of confusion in the mineralogical data about manganese nodules. The most frequent manganese mineral in deep-sea manganese nodules is an 10 A manganate... 

More than 20 manganese oxide phases have been described from continental manganese deposits, but very few of these minerals have been positively identified from marine environments (Table 3). Useful summaries of the nature and nomenclature of the marine manganese minerals include those of Cronan (1976b), R. G. Bums and V. M. Burns (1979), and Post (1999). Marine manganese oxides are hydrous phases usually with poor crystallinity. They are often intimately intergrown with other phases, particularly iron-oxy-hydroxides and hydrous iron oxides. Marine manganese-oxide minerals host a variety of minor elements of economic... 

Ferromanganese Nodules and Crusts Table 3 Manganese minerals in marine Mn nodules and crusts. 

The high capacity of manganese oxides for the sorption of cations leads to an enrichment of manganese-rich sediments in a number of economically valuable transition metals, particularly copper, nickel, and cobalt. However, the exact mechanism of the incorporation of these metals remains controversial. For example, R. G. Burns and M. Burns (1977a) maintained that these elements substitute within the lattice of the manganese minerals, whereas Glasby (1974)... 

Common Manganese Minerals 7.11.4 COMMON MANGANESE MINERALS... 

Cronan D. S. (1997) Some controls on the geochemical variabihty of manganese nodules with particular reference to the tropical South Pacific. In Manganese Mineralization Geochemistry and Mineralogy of Terrestrial and Marine Deposits, Special Publication Number 119 (eds. K. Nicholson, J. R. Hein, B. Biihn, and S. Dasgupta). Geological Society of London, pp. 139-152. 

Maynard J. B., Okita P. M., May E. D., and Martinez-Vera A. (1990) Palaeogeographic setting of Fate Jurassic manganese mineralization in the Molango District, Mexico. In Sediment Hosted Mineral Deposits, International Association of Sedimentologists, Special Publication 11 (eds. J. Parnell, L.-J. Ye, and C.-M. Chen). Blackwell, Boston, pp. 17-30. 

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