Red and black were the two colours around which Palaeolithic art was organised. Manganese oxides and charcoal were the black pigments and hematite (α-Fe 2 O 3 ) the red one. The latter mineral is naturally abundant, but archaeological observations nevertheless suggest that the well-known colour change accompanying the dehydration of yellow goethite (α-FeOOH) to red hematite may have been employed by Prehistoric artists to obtain red pigment. In order to confirm this assumption, a study was carried out on synthetic goethite samples using XRD and TEM. In particular, the goethite-to-hematite transformation was observed in situ and provided useful information about both dehydration and recrystallisation processes. The existence of water up to high heating temperatures was found to be coherent with the typical porous microstructure accompanying the phase transformation. Similar studies were carried out on archaeological hematites coming from Troubat, a French Pyrenean Palaeolithic site. Characteristic features of previous heating were identified, such as pores or small amounts of maghemite (α-Fe 2 O 3 ), which confirms that Prehistorics had acquired this technical know-how.

Tem observations of goethite dehydration: application to archaeological samples

Physical speciation of trace metals in Fe–Mn concretions from a rendzic lithosol developed on Sinemurian limestones (France)

Hydration of the β-MnO2 (110), (100), and (101) surfaces is investigated using a combination of periodic density functional theory and ab initio thermodynamics. Fully hydrated surfaces are found to be significantly more stable than the stoichiometric ones up to temperatures in the range of 650 to 730 K at ambient oxygen and water partial pressures. A mixture of molecular and dissociative water adsorption is predicted to occur on the (110) and (101) surfaces, while the (100) surface does not dissociate water. Changes in surface reactivity upon water adsorption are explored via partial density of states analysis. Differences in surface relaxations and vibrational spectra are discussed and can be used to identify the type of adsorption mode.

Structure and Stability of Hydrated β-MnO2 Surfaces

The objective of this study was to describe the proton promoted disproportion of synthetic manganite (gamma-MnOOH) and to characterise the resulting phase transformations. The solution and remainin ...

Phase Transformations and Proton Promoted Dissolution of Hydrous Manganite (γ-MnOOH)

Results of thermic transformations of ore minerals from genetically different oceanic ferromanganese rocks in the course of their heating up to 1000°C are considered. Manganese minerals with various types of crystalline lattice have different grades of thermic stability. Layered manganese minerals (buserite I, asbolane-buserite, and birnessite) are stable up to 120–150°C; asbolane up to 180°C, vernadite, up to ∼500°C; todorokite and pyrolusite (minerals of the tunnel group), up to 600 and 670°C, respectively. Sorbed cations of heavy metals govern the transformation temperature and mineral composition of products of the calcination of ferromanganese rocks. Study of birnessite and todorokite demonstrated that genesis of ferromanganese rocks do not affect thermic properties of minerals in them.

Transformations of ore minerals in genetically different oceanic ferromanganese rocks

Unheated natural mixtures of manganite and secondary pyrolusite, from the same lateritic manganiferous sequence, were studied in different orientations by high-resolution transmission electron microscopy (HRTEM), electron diffraction, and energy-dispersive X-ray analysis (EDX) to determine the fine structure of these phases, their possible crystallographic relations, and the genetic processes that led to the formation of the pyrolusite. Typical palisadic texture was observed for both minerals. Characteristic cracks parallel t. (010) of the pyrolusite structure and in particular microfissures in manganite were noted as signs of structural accommodation accompanying the transformation phenomenon between these two minerals. A previously unreported manganese oxide of the spinel-type (γ-Mn2O3 or Mn3O4) was also identified in the original mixture. This oxide gave pure microdomains as intergrowths with pyrolusite adjacent to manganite. This is the first report of a natural occurrence of γ-Mn2O3. The manganite-pyrolusite transformation process and an unsuspected γ-Mn2O3 (Mn3O4)-pyrolusite transition were directly illustrated in detail for the first time. Interfaces between the concerned phases were not sharp or smooth, but exhibited strong strain contrasts and interferential periodicities. Lattice images and microdiffraction patterns proved that both transformations were oriented, suggestive of topotactic relations. In addition, the principal minerals in the matrix (illite, kaolinite, and goethite) were examined for a better understanding of their role in Mn-oxyhydroxides transformations.

High-resolution transmission electron microscopy study of Mn-oxyhydroxide transformations and accompanying phases in a lateritic profile of Moanda, Gabon

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

D. Nahon

Author Tools

Chat about Author

Papers

High-resolution transmission electron microscopy study of Mn-oxyhydroxide transformations and accompanying phases in a lateritic profile of Moanda, Gabon