Dataset Information

Clay minerals identification in rock varnish by XRD: A one-step reduction approach

ABSTRACT: Rock varnishes are known to be fine, dark, glossy submicron films found in deserts bare rock surfaces. The oxides and hydroxides of manganese and iron bind together the clay minerals present in the varnish layer. The processes of oxide-hydroxide accumulation at varnish sites are due to iron and manganese oxidizing bacteria which may require clay minerals for additional nutrition. Quantification and identification of clay minerals in this biofilm is needed to understand its formation. Past attempts to analyze the mineralogical composition of rock varnish have led to inconclusive results as varnish is a submicron thin layer composed of a complex mineral matrix. The elimination of non-crystalline cementing groups comprising of free iron oxides is a key step in the identification of many types of clay minerals, particularly in soil/sediment mineral studies.• The Fe-Mn oxide-hydroxide coatings, acting as cementing materials, can be easily removed using a one-step reduction method employing Na2S2O4 at 70 °C, leading to separation of clay minerals.• We have taken the lead from earlier reported Jackson (1958) method, wherein a combination of reagents was used such as sodium acetate, sodium citrate, hydrogen peroxide, sodium bicarbonate, and sodium dithionite for removing carbonate, organic carbon and Fe-Mn oxy-hydroxide coatings respectively from sediment grains to segregate individual grains from each other.• Our modification helps in the unveiling of clay minerals from a solid substrate and reports the X-ray diffraction peaks, which are elsewise hard to detect and therefore earlier studies are inconclusive. Graphical Abstract *Abbreviations – Qtz – Quartz, Pl – Plagioclase, Fds – Feldspar, Bt – Biotite and Hbl – Hornblende.Image, graphical abstract

SUBMITTER: Chaddha A

PROVIDER: S-EPMC8563653 | biostudies-literature |

REPOSITORIES: biostudies-literature

ACCESS DATA

Similar Datasets

Project description:Rock varnish is a thin coating enriched with manganese (Mn) and iron (Fe) oxides. The mineral composition and formation of rock varnish elicit considerable attention from geologists and microbiologists. However, limited research has been devoted to the semiconducting properties of these Fe/Mn oxides in varnish and relatively little attention is paid to the mineral-microbe interaction under sunlight. In this study, the mineral composition and the bacterial communities on varnish from the Gobi Desert in Xinjiang, China were analyzed. Results of principal components analysis and t-test indicated that more electroactive genera such as Acinetobacter, Staphylococcus, Dietzia, and Pseudomonas gathered on varnish bacterial communities than on substrate rock and surrounding soils. We then explored the culture of varnish, substrate and soil samples in media and the extracellular electron transfer (EET) between bacterial communities and mineral electrodes under light/dark conditions for the first time. Orthogonal electrochemical experiments demonstrated that the most remarkable photocurrent density of 6.1 ± 0.4 μA/cm2 was observed between varnish electrode and varnish microflora. Finally, based on Raman and 16S rRNA gene-sequencing results, coculture system of birnessite and Pseudomonas (the major Mn oxide and a common electroactive bacterium in varnish) was established to study underlying mechanism. A steadily growing photocurrent (205 μA at 100 h) under light was observed with a stable birnessite after 110 h. However, only 47 μA was generated in the dark control and birnessite was reduced to Mn2+ in 13 h, suggesting that birnessite helped deliver electrons instead of serving as an electron acceptor under light. Our study demonstrated that electroactive bacterial communities were positively correlated with Fe/Mn semiconducting minerals in varnish, and diversified EET process occurred on varnish under sunlight. Overall, these phenomena may influence bacterial-community structure in natural environments over time.

Dataset Information

Clay minerals identification in rock varnish by XRD: A one-step reduction approach

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets