Beitrag zur Kenntnis der Mangan(II)‐manganite und des δ‐MnO<sub>2</sub>

Buser, Walter; Graf, Patricia; Feitknecht, W.

doi:10.1002/hlca.19540370746

Cited by 108 publications

(46 citation statements)

References 15 publications

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“…The two K positions per unit cell are only half filled, because the short K-K distance of 0.28 nm will make the structure unstable due to repulsive forces between the cations if all of the K sites are filled (Bystörm and Bystörm, 1950). The upper limit for potassium in cryptomelane is about 7 wt%, while the lower limit lies between 0.25 wt% and 2.2 wt%K (Burser et al, 1954;McKenzie, 1971). Cryptomelane have several 2 × 2 tunnel structure analogues in nature.…”

Section: Discussionmentioning

confidence: 99%

The mineralogical characterization of argentian cryptomelane from Xiangguang Mn–Ag deposit, North China

Fan

Wang

Xing-tao

et al. 2015

Journal of Mineralogical and Petrological Sciences

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Argentian cryptomelane as a quite rare variety is determined during the investigation of Mn-Ag ore samples from Xiangguang deposit along the northern margin of North China craton. The mineral observed by a polarizing petrographic microscope involves concentric ring-band, pisolitic and veinlet structures and greyish white color. The scanning electron microscopy reveals a large number of elongated nanocrystals in the forms of nanofibers and nanorods in this densely natural argentian cryptomelane. The specifically chemical features in two samples of XG-C-1 and XG-C-2 of cryptomelane are: (1) The silver content ranges from about 0.22-3.15 wt%, which is much higher than that of other manganese oxides including ranciéite, chalcophanite and coronodite found in this deposit as well. Both of two argentian cryptomelane samples feature two main Raman scattering contributions at about 580 cm −1 and 630 cm −1 , belonging to the Mn-O lattice vibrations within the MnO 6 octahedral double chains, which can distinguish from other three manganese oxides. The Ag + prefers to locate in the tunnel sites substituting K + of cryptomelane due to its large radius and the same monovalent state with K + . Some chain-width disorders characterized by transmission electron microscopy are probably caused by these cation substitutions.

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Section: Discussionmentioning

confidence: 99%

The mineralogical characterization of argentian cryptomelane from Xiangguang Mn–Ag deposit, North China

Fan

Wang

Xing-tao

et al. 2015

Journal of Mineralogical and Petrological Sciences

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“…The transmission micrograph of the experimental sample was similar to that shown by McKenzie (1989) for cryptomelane, which appeared as lath-shaped crystals. Also, the conversion ofbirnessite to cryptomelane has been achieved by several workers (Buser and Feitknecht, 1954;Gattow and Glemser, 1961;Glemser et aL, 196 I) by directly igniting synthetic birnessite at 400~ or boiling birnessite that had been prewashed with MnSO4 solution or dilute HCI. The lath-shaped crystals (CR in Figure lc), about 0.4/~m in length, were most likely crymptomelane.…”

Section: Transformation Of Birnessite As Affected By Mns04 At Differementioning

confidence: 99%

Transformations of Synthetic Birnessite as Affected by pH and Manganese Concentration

1994

Clays and clay miner.

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AImtract--The amount of Mn 2+ adsorbed or removed from solution by birnessite is several times greater than its reported cation exchange capacity. Extractability of the sorbed Mn 2+ decreases with aging. It is uncertain whether the sorbed Mn 2+ is oxidized on the surface or incorporated into the structure of birnessite. Using X-ray powder diffractometry and transmission electron microscopy, a study was conducted to examine the mineralogical alteration of birnessite after treatment with various concentrations of MnSO4 and solution pH.The sorbed Mn 2+ was not directly oxidized and remained on the birnessite surface. The sorption of Mn 2+ was followed by alteration ofbirnessite with the formation of new Mn minerals. The specific Mn minerals formed were governed by the pH of the reaction, and the rate of the transformation was determined by Mn 2+ concentration and pH. Nsutite and ramsdellite were identified at pH 2.4, cryptomelane at pH 4, groutite at pH 6, and mangarfite at pH 8. Other Mn minerals formed at these and other pH levels could not be identified. As the concentration of Mn in the solution decreased, the time required to form new minerals from the birnessite increased. The newly formed phases were the result of structural conversion since dissolution of birnessite and reprecipitation of new phases were not observed.

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“…It is reasonable to expect that some large A ions are necessary to prevent collapse of the framework, ct-MnO2 for example can be prepared only in the presence of a large ion such as K +. The cubic coordinated sites in the tunnels are seldom more than half-filled but may be almost entirely empty [Buser, Graf & Feitknecht (1954) reported the a-MnO 2 structure retained for a K ÷ : Mn 4+ ratio of 1 : 70].…”

Section: Structural Background (A) Hollandite Group Of Structuresmentioning

confidence: 99%

Structural relationships between β-gallia, rutile, hollandite, psilomelane, ramsdellite and gallium titanate type structures

Bursill¹

1979

Acta Crystallogr Sect B

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The relationships between the above structure types are considered theoretically. New types of tunnel structures and transformation mechanisms are derived. The analysis predicts many variations of the hollandite structure type previously unsuspected. These go some way towards explaining the indefinite structural results obtained using X-ray diffraction techniques for hollandite and related minerals and also for ),-manganese oxides and hydroxides. It is strongly suggested that preparative and characterization techniques need to be far more thorough and penetrating than those used so far, if significant measurements of physical properties, such as superionic conductivity, are to be made.

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Beitrag zur Kenntnis der Mangan(II)‐manganite und des δ‐MnO₂

Cited by 108 publications

References 15 publications

The mineralogical characterization of argentian cryptomelane from Xiangguang Mn–Ag deposit, North China

The mineralogical characterization of argentian cryptomelane from Xiangguang Mn–Ag deposit, North China

Transformations of Synthetic Birnessite as Affected by pH and Manganese Concentration

Structural relationships between β-gallia, rutile, hollandite, psilomelane, ramsdellite and gallium titanate type structures

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Beitrag zur Kenntnis der Mangan(II)‐manganite und des δ‐MnO2

Cited by 108 publications

References 15 publications

The mineralogical characterization of argentian cryptomelane from Xiangguang Mn–Ag deposit, North China

The mineralogical characterization of argentian cryptomelane from Xiangguang Mn–Ag deposit, North China

Transformations of Synthetic Birnessite as Affected by pH and Manganese Concentration

Structural relationships between β-gallia, rutile, hollandite, psilomelane, ramsdellite and gallium titanate type structures

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Beitrag zur Kenntnis der Mangan(II)‐manganite und des δ‐MnO₂