The manganese oxide mineral, lithiophorite, in an oxisol From Hawaii

Abstract

The mineralogical composition of the surface soil horizon (0-15 cm) of Wahiawa soil (Tropeptic Eutrustox) was investigated by X-ray diffraction (XRD), high gradient magnetic separation (HGMS), transmission electron microscopy (TEM), and infrared methods. The concentration of lithiophorite decreased with particle size and none was present in the clay fraction as indicated by XRD. Lithiophorite was further concentrated from the crushed sand-sized fraction by HGMS. Hexagonal, electron-dense, often twinned lithiophorite particles were identified by electron diffraction. Differential infrared (DIR) spectra obtained by dissolving Mn oxides in acidified hydroxylamine hydrochloride (HAHC) indicated lithiophorite as the HAHC-soluble Mn-phase. Lithiophorite compositiion, as revealed by chemical analysis of the HAHC extracts, consisted of appreciable amounts of Mn, Al, Zn, Co and Mg, and less than stoichiometric amounts of Li. Sodium hydroxide treatment apparently altered the lithiophorite, as revealed by the DIR spectrum of the hydroxylamine-soluble fraction of the NaOH-treated sample compared with the untreated sample. The high crystallinity of the lithiophorite was suggested by its resistance to chemical dissolution and narrow X-ray diffraction lines. No evidence for the presence of todorokite or birnessite was found, contrary to earlier reports. Examination of sand-sized nodules by scanning electron microscopy indicated large (2-5 �m) platy lithiophorite crystals at the surface of these nodules. Electron microprobe analysis of these platy particles indicated iron enrichment near the surface. The freshly fractured nodule surface revealed numerous unaltered platy crystals of lithiophorite filling the veins of the nodule.

Morphological, chemical and mineralogical properties of some manganese-rich oxisols derived from dolomite in Mpumalanga province, South Africa

“…3) suggests that Mn oxide (chiefly lithiophorite on the basis of XRD evidence), which pigments the fine earth fraction in the lower solum, has been dissolved by reduction in the upper solum and reprecipitated by oxidation to form nodules. Towards the surface, both more acidic conditions (Table 3) and a greater abundance of organic matter as an energy substrate (Table 2) would promote the reductive dissolution of lithiophorite which may also result in residual enrichment of Al as gibbsite similar to that found in manganese-rich oxisols of Hawaii (Golden et al, 1993). Relocation of Fe into the nodule fraction is also evident in an upward direction ( Fig.…”

“…The Al in the structure of lithiophorite appears to enhance its stability. In the weathering sequence of Mn oxides, lithiophorite is considered the final weathering product (Dixon, 1988;Parc et al, 1989) and eventually transforms to gibbsite through reductive dissolution (Golden et al, 1993). Lithiophorite has been demonstrated as being a weaker oxidizing agent than other Mn oxides (Kim et al, 2002;Neaman et al, 2004), which has been attributed to a higher proportion of Mn 3+ in the structure (Kim et al, 2002).…”

“…5). Lithiophorite has been identified as the most stable Mn oxide in acid, highly weathered soils (Taylor et al, 1964) and this has been attributed (Golden et al, 1993) to the fact that high Al concentrations are needed for its formation. Another possibility is that gibbsite sheets reduce the activation energy for Mn oxidation and act as templates for lithiophorite crystallization when Mn is dissolved from less stable minerals.…”

Manganese oxide minerals: Crystal structures and economic and environmental significance

“…It has been noted that frequently observed influences of pH, organic matter, lime, and phosphate on heavy metal availability in soils are understood principally in terms of their influence on the chemistries of hydrous oxides of Mn and Fe (28). The major Mn minerals reported in soils are lithiophorite, hollandite, and birnessite (39,40); it is more typically the case, however, that because the Mn oxides are fine-grained and poorly crystalline (commonly referred to as amorphous) that no attempt is made to assign mineral designations.…”

Óxidos de manganês em solos do quadrilátero ferrífero (MG)

“…(Kämpf et al, 2009), o que a distingue da caulinita nesta faixa do difratograma de raios X, cujo reflexo (020) deste argilomineral corresponde a 0,447 nm. A inferir-se pela relativa pouca expressividade da gibbsita, a presença de litioforita no Ex03 provavelmente esteja relacionada à maior disponibilidade de Al, cuja presença em altos teores é considerada necessária para sua formação (Golden et al, 1993).…”