Micro- to nano-scale characterization of martite from a banded iron formation in India and a lateritic soil in Brazil

Abstract

Indian crystals show trellis of subhedral magnetite hosting maghemite in sharp contact with interstitial hematite crystals, which suggests exsolution along parting planes. grain boundary migrations within the hematite point to dynamic crystallization during deformation. Dislocations and fluid inclusions in hematite reflect its precipitation related to a hydrothermal event. In the Brazilian martite, dislocations are observed and maghemite occurs as Insel structures and nano-twin sets. The latter, typical for the hematite, are a transformation product from maghemite into hematite. For both samples, a deformation-induced hydrothermally driven transformation from magnetite via maghemite to hematite is proposed. The transformation from magnetite into maghemite comprises intermediate non-stoichiometric magnetite steps related to a redox process. This study shows that martite found in supergene environment may result from earlier hypogene processes.

Characterization of Ferrospheres Recovered from High-Calcium Fly Ash

“…31,32 The mechanism of martitization has so far been poorly investigated. According to Orberger et al, 33 The SEM images of the sections of globules with a single-block structure (Figure 6c,d) demonstrate that the globules consist of an array of ferrospinel blocks, which contain sub-micrometerand micrometer-sized pores and interfaces of blocks. The martitization of globule 2182 occurs predominantly near the surface and propagates deep into the bulk along the block boundaries (Figure 6a).…”

Synthesis and Characterization of Amorphous Iron Oxide Nanoparticles by the Sonochemical Method and Their Application for the Remediation of Heavy Metals from Wastewater

“…In Figure 3, the Raman spectrum reveals the three characteristic peaks of IONPs i.e., 273, 488, and 691 cm −1 , which could be due to the mixed phases of magnetite and maghemite. These mixed phases here could also be due to the utilization of high energy laser beam which may oxidize the magnetite phase and may become transformed into the maghemite phase by a phenomenon called martitization [58].…”

Rapid light carbon releases and increased aridity linked to Karoo–Ferrar magmatism during the early Toarcian oceanic anoxic event

“…Rather, the close relationship between the sediment color, increased Hg contents and δ 13 C org shifts suggests that magnetic enhancement and the presence of martite are the consequence of climate and environmental changes triggered by magmatic activity of the Karoo-Ferrar LIP. Martitization is a widespread phenomenon in various geological settings, however the processes involved in its formation are not fully understood (e.g., 75 , 77 ). Martite occurs in banded iron formations, ore deposits and continental red beds but has been rarely described in marine hemipelagic sediments such as those studied here.…”

“…The transformation of magnetite into hematite has been considered a redox reaction linked to increased oxygen fugacity. However, the oxygen fugacity in many geologic environments is deemed too low to account for hematite formation via classic redox reactions, leading some authors to consider non-redox formation reactions involving the leaching of Fe 2+ ions by acidic solutions 75 , 77 , 78 . Although oxygen fugacity is relatively low in hemipelagic and pelagic settings, redox transformation of magnetic minerals may occur in some organic-rich marine sediments.…”