scholarly journals Biomineralization of dolomite and magnesite discovered in tropical coralline algae: a biological solution to the geological dolomite problem

2011 ◽  
Vol 8 (3) ◽  
pp. 5881-5906 ◽  
Author(s):  
M. C. Nash ◽  
U. Troitzsch ◽  
B. N. Opdyke ◽  
J. M. Trafford ◽  
B. D. Russell ◽  
...  
Keyword(s):  
Crustose Coralline Alga ◽  
Coralline Algae ◽  
X Ray Diffraction ◽  
Sedimentary Environments ◽  
Mineral Phases ◽  
Magnesium Calcite ◽  
Tropical Reef ◽  
Dolomite Problem ◽  
Geologic Record ◽  
Micro Analysis

Abstract. Dolomite is a magnesium-rich carbonate mineral abundant in fossil carbonate reef platforms but surprisingly rare in modern sedimentary environments, a conundrum known as the ''Dolomite Problem". Marine sedimentary dolomite has been interpreted to form by an unconfirmed, post-depositional diagenetic process, despite minimal experimental success at replicating this. Here we show that dolomite, accompanied by magnesite, forms within living crustose coralline alga, Hydrolithon onkodes, a prolific global tropical reef species. Chemical micro-analysis of the coralline skeleton reveals that not only are the cell walls calcitised, but that cell spaces are typically filled with magnesite, rimmed by dolomite, or both. Mineralogy was confirmed by X-ray diffraction. Thus there are at least three mineral phases present (magnesium calcite, dolomite and magnesite) rather than one or two (magnesium calcite and brucite) as previously thought. Our results are consistent with dolomite occurrences in coralline algae rich environments in fossil reefs. Instead of a theory of post-depositional dolomitisation, we present evidence revealing biomineralization that can account for the massive formations seen in the geologic record. Additionally, our findings imply that previously unrecognized dolomite and magnesite have formed throughout the Holocene. This discovery together with the scale of coralline algae dominance in past shallow carbonate environments raises the possibility that environmental factors driving this biological dolomitisation process have influenced the global marine magnesium/calcium cycle. Perhaps, most importantly, we reveal that what has been considered a geological process can be a biological process, having many implications for both disciplines.

scholarly journals First discovery of dolomite and magnesite in living coralline algae and its geobiological implications

2011 ◽  
Vol 8 (11) ◽  
pp. 3331-3340 ◽  
Author(s):  
M. C. Nash ◽  
U. Troitzsch ◽  
B. N. Opdyke ◽  
J. M. Trafford ◽  
B. D. Russell ◽  
...  
Keyword(s):  
Crustose Coralline Alga ◽  
Coralline Algae ◽  
X Ray Diffraction ◽  
Sedimentary Environments ◽  
Mineral Phases ◽  
Magnesium Calcite ◽  
Tropical Reef ◽  
Dolomite Problem ◽  
Diffraction Patterns ◽  
Micro Analysis

Abstract. Dolomite is a magnesium-rich carbonate mineral abundant in fossil carbonate reef platforms but surprisingly rare in modern sedimentary environments, a conundrum known as the "Dolomite Problem". Marine sedimentary dolomite has been interpreted to form by an unconfirmed, post-depositional diagenetic process, despite minimal experimental success at replicating this. Here we show that dolomite, accompanied by magnesite, forms within living crustose coralline alga, Hydrolithon onkodes, a prolific global tropical reef species. Chemical micro-analysis of the coralline skeleton reveals that not only are the cell walls calcitised, but that cell spaces are typically filled with magnesite, rimmed by dolomite, or both. Mineralogy was confirmed by X-ray Diffraction. Thus there are at least three mineral phases present (magnesium calcite, dolomite and magnesite) rather than one or two (magnesium calcite and brucite) as previously thought. Our results are consistent with dolomite occurrences in coralline algae rich environments in fossil reefs of the last 60 million years. We reveal that the standard method of removing organic material prior to Xray Diffraction analysis can result in a decrease in the most obvious dolomite and magnesite diffraction patterns and this may explain why the abundant protodolomite and magnesite discovered in this study has not previously been recognized. This discovery of dolomite in living coralline algae extends the range of palaeo-environments for which biologically initiated dolomite can be considered a possible source of primary dolomite.

scholarly journals Mineralogical response of the Mediterranean crustose coralline alga <i>Lithophyllum cabiochae</i> to near-future ocean acidification and warming

2016 ◽  
Author(s):  
Merinda C. Nash ◽  
Sophie Martin ◽  
Jean-Pierre Gattuso
Keyword(s):  
Ocean Acidification ◽  
Crustose Coralline Alga ◽  
Coralline Algae ◽  
Coralline Alga ◽  
Magnesium Calcite ◽  
The Mediterranean ◽  
One Year ◽  
The Stability ◽  
Strong Control ◽  
Near Future

Abstract. Red calcareous coralline algae are thought to be among organisms the most vulnerable to ocean acidification due to the high solubility of their magnesium calcite skeleton. Although, skeletal mineralogy is proposed to change as CO2 and temperature continues rising, there is currently very little information available on the response of coralline algal carbonate mineralogy to near-future changes in pCO2 and temperature. Here we present results from a one-year controlled laboratory experiment to test mineralogical responses to pCO2 and temperature in the Mediterranean crustose coralline alga (CCA) Lithophyllum cabiochae. Our results show that Mg incorporation is mainly constrained by temperature (+1 mol% MgCO3 for an increase of 3 °C) and there was no response to pCO2. This suggests that L. cabiochae thalli have the ability to buffer calcifying medium against ocean acidification, enabling them to continue to deposit Mg-calcite with a significant mol% MgCO3 under elevated pCO2. Analyses of CCA dissolution chips showed a decrease in Mg content after 1 year for all treatments but this was not affected by pCO2 nor by temperature. Our findings suggest that biological processes exert a strong control on calcification on Mg-calcite and that CCA may be more resilient under rising CO2 than previously thought. However, previously demonstrated increased skeletal dissolution with ocean acidification will still have major consequences for the stability and maintenance of Mediterranean coralligenous habitats.

scholarly journals Mineralogical response of the Mediterranean crustose coralline alga <i>Lithophyllum cabiochae</i> to near-future ocean acidification and warming

2016 ◽  
Vol 13 (21) ◽  
pp. 5937-5945 ◽  
Author(s):  
Merinda C. Nash ◽  
Sophie Martin ◽  
Jean-Pierre Gattuso
Keyword(s):  
Ocean Acidification ◽  
Crustose Coralline Alga ◽  
Coralline Algae ◽  
Coralline Alga ◽  
Magnesium Calcite ◽  
The Mediterranean ◽  
The Stability ◽  
Strong Control ◽  
Mg Content ◽  
Near Future

Abstract. Red calcareous coralline algae are thought to be among the organisms most vulnerable to ocean acidification due to the high solubility of their magnesium calcite skeleton. Although skeletal mineralogy is proposed to change as CO2 and temperature continue to rise, there is currently very little information available on the response of coralline algal carbonate mineralogy to near-future changes in pCO2 and temperature. Here we present results from a 1-year controlled laboratory experiment to test mineralogical responses to pCO2 and temperature in the Mediterranean crustose coralline alga (CCA) Lithophyllum cabiochae. Our results show that Mg incorporation is mainly constrained by temperature (+1 mol % MgCO3 for an increase of 3 °C), and there was no response to pCO2. This suggests that L. cabiochae thalli have the ability to buffer their calcifying medium against ocean acidification, thereby enabling them to continue to deposit magnesium calcite with a significant mol % MgCO3 under elevated pCO2. Analyses of CCA dissolution chips showed a decrease in Mg content after 1 year for all treatments, but this was affected neither by pCO2 nor by temperature. Our findings suggest that biological processes exert a strong control on calcification on magnesium calcite and that CCA may be more resilient under rising CO2 than previously thought. However, previously demonstrated increased skeletal dissolution with ocean acidification will still have major consequences for the stability and maintenance of Mediterranean coralligenous habitats.

scholarly journals Mineral Phases in Carbonate Rocks of the Górażdże Beds from the Area of Opole Silesia

2016 ◽  
Vol 32 (3) ◽  
pp. 67-92
Author(s):  
Katarzyna Stanienda
Keyword(s):  
Ftir Spectroscopy ◽  
Microscopic Analysis ◽  
X Ray Diffraction ◽  
Geochemical Composition ◽  
X Ray ◽  
Rock Samples ◽  
Low Magnesium ◽  
Mineral Phases ◽  
Magnesium Calcite ◽  
High Magnesium Calcite

AbstractThis article presents the results of studies of carbonate rock samples that came from all members of the Górażdże Beds (Lower Muschelkalk – Middle Triassic), taken from the area of the Opole Silesia. Researches allowed the types of mineral phases which built the analyzed rocks to be determined. The limestone samples were collected in the Ligota Dolna Quarry, Strzelce Opolskie Quarry, Wysoka Quarry and the area of Saint Anne Mountain. Thirteen samples were taken from the Ligota Dolna Deposit, 4 samples – in the Strzelce Opolskie Quarry and 5 samples – in the area of St. Anne Mountain. Selected rock samples were examined using a microscope with polarized, transmitted light, FTIR spectroscopy, X-ray diffraction and microprobe measurements E PMA.The results of the study show that the limestone of the Górażdże Beds from the area of Opole Silesia do not exhibit diversified types according to the Ca and Mg content of. They are characterized by the Ca and Mg high purity of geochemical composition, as well as the domination of the low magnesium calcite. There are lower contents of carbonate phases rich in magnesium – high magnesium calcite (high-Mg calcite, which is also known as magnesio-calcite) and dolomite. The majority of the data was obtained through the results of the FTIR spectroscopy and microprobe measurements. Some information gave the results of microscopic analysis. The results of X-ray diffraction indicate the occurrence only low magnesium calcite in the studied samples. Dolomite was identified in some samples of Górażdże Beds and high magnesium calcite – in sample of the Wysoka Micrite Member. Smaller amounts of non-carbonate phases occurred in the analyzed rocks. Quartz, chalcedony, feldspars, micas and clay minerals were identified among the non-carbonate phases.The small diversification of the geochemical composition of the Górażdże limestones could be connected with their sedimentation environment conditions. These rocks represent the type of barrier sediments, which were formed during the sea transgression.

scholarly journals First Report on the Geologic Occurrence of Natural Na–A Zeolite and Associated Minerals in Cretaceous Mudstones of the Paja Formation of Vélez (Santander), Colombia

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 218
Author(s):  
Carlos Alberto Ríos-Reyes ◽  
German Alfonso Reyes-Mendoza ◽  
José Antonio Henao-Martínez ◽  
Craig Williams ◽  
Alan Dyer
Keyword(s):  
Natural Zeolite ◽  
Scanning Electron Micrographs ◽  
Total Sulfur ◽  
Zeolite A ◽  
X Ray Diffraction ◽  
X Ray ◽  
Mineral Phases ◽  
The World ◽  
Porosity And Permeability ◽  
First Time

This study reports for the first time the geologic occurrence of natural zeolite A and associated minerals in mudstones from the Cretaceous Paja Formation in the urban area of the municipality of Vélez (Santander), Colombia. These rocks are mainly composed of quartz, muscovite, pyrophyllite, kaolinite and chlorite group minerals, framboidal and cubic pyrite, as well as marcasite, with minor feldspar, sulphates, and phosphates. Total organic carbon (TOC), total sulfur (TS), and millimeter fragments of algae are high, whereas few centimeters and not biodiverse small ammonite fossils, and other allochemical components are subordinated. Na–A zeolite and associated mineral phases as sodalite occur just beside the interparticle micropores (honeycomb from framboidal, cube molds, and amorphous cavities). It is facilitated by petrophysical properties alterations, due to processes of high diagenesis, temperatures up to 80–100 °C, with weathering contributions, which increase the porosity and permeability, as well as the transmissivity (fluid flow), allowing the geochemistry remobilization and/or recrystallization of pre-existing silica, muscovite, kaolinite minerals group, salts, carbonates, oxides and peroxides. X-ray diffraction analyses reveal the mineral composition of the mudstones and scanning electron micrographs show the typical cubic morphology of Na–A zeolite of approximately 0.45 mμ in particle size. Our data show that the sequence of the transformation of phases is: Poorly crystalline aluminosilicate → sodalite → Na–A zeolite. A literature review shows that this is an unusual example of the occurrence of natural zeolites in sedimentary marine rocks recognized around the world.

AIN/GaN and AIGaN/GaN Heterostructures Grown by HVPE on SiC Substrates

1997 ◽  
Vol 482 ◽  
Author(s):  
Yu. V. Melnik ◽  
A. E. Nikolaev ◽  
S. I. Stepanov ◽  
A. S. Zubrilov ◽  
I. P. Nikitina ◽  
...  
Keyword(s):  
Growth Rate ◽  
Electron Beam ◽  
Vapor Phase ◽  
Electron Spectroscopy ◽  
Auger Electron ◽  
Hydride Vapor Phase Epitaxy ◽  
X Ray Diffraction ◽  
Electrical Measurements ◽  
X Ray ◽  
Micro Analysis

AbstractGaN, AIN and AIGaN layers were grown by hydride vapor phase epitaxy. 6H-SiC wafers were used as substrates. Properties of AIN/GaN and AIGaN/GaN structures were investigated. AIGaN growth rate was about 1 μm/min. The thickness of the AIGaN layers ranged from 0.5 to 5 μm. The AIN concentration in AIGaN layers was varied from 9 to 67 mol. %. Samples were characterised by electron beam micro analysis, Auger electron spectroscopy, X-ray diffraction and cathodoluminescence.Electrical measurements performed on AIGaN/GaN/SiC samples indicated that undoped AIGaN layers are conducting at least up to 50 mol. % of AIN.

Deterioration of concrete containing limestone powder exposed to sulfate attack at ambient temperature

2021 ◽  
Vol 11 (5) ◽  
pp. 724-731
Author(s):  
Hemin Liu ◽  
Qian Huang ◽  
Liang Zhao
Keyword(s):  
Ambient Temperature ◽  
Sulfate Solution ◽  
Sulfate Attack ◽  
Limestone Powder ◽  
X Ray Diffraction ◽  
X Ray ◽  
Mineral Phases ◽  
Adverse Influence ◽  
Powder Content ◽  
Scanning Electron

This study investigates the deterioration of concrete containing limestone powder exposed to sulfate solution under ambient temperature (20~25 °C). Microstructure and mineral phases within the attacked concrete were measured by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). It was found that the addition of limestone powder increased the initial porosity of concrete. Consequently, a larger amount of SO2–4 ions diffused into the concrete containing limestone powder, and their degree of deterioration caused by sulfate attack increased with the increase in limestone powder content. At ambient temperature, gypsum and ettringite were the major attack products, respectively within the surface and nearsurface portions of concrete containing limestone powder, which was consistent with the products of sulfate attack within concrete without limestone powder. Therefore, the type and distribution of the attack products in concrete had not been revised due to the addition of limestone powder. Nevertheless, the adverse influence of limestone powder on the sulfate resistance of concrete, even at ambient temperature, should be considered. Furthermore, effective measures should be implemented to improve the durability of concrete containing limestone powder in this environment.

scholarly journals Influence of Mineral Admixtures on Corrosion Inhibition Effect of Nitrites

2018 ◽  
Vol 2018 ◽  
pp. 1-6 ◽  
Author(s):  
Mengna Yang ◽  
Junzhe Liu ◽  
Hui Wang ◽  
Yushun Li ◽  
Yanhua Dai ◽  
...  
Keyword(s):  
Fly Ash ◽  
Corrosion Inhibition ◽  
Ion Concentration ◽  
Mineral Admixtures ◽  
X Ray Diffraction ◽  
Nitrite Ion ◽  
X Ray ◽  
Inhibition Effect ◽  
Diffraction Patterns ◽  
Micro Analysis

Chemical quantitative analysis of effective anticorrosion component and micro-analysis of hydration products of fly ash and slag on the influence of the nitrites corrosion inhibition was studied by the free nitrite ion concentration and X-ray diffraction pattern. The free nitrite ion concentration was used to describe the corrosion inhibition effect of nitrites. And the X-ray diffraction patterns were used to analyze the adsorption properties. The research results show that fly ash and slag were beneficial for improving the corrosion inhibition effect of nitrites. Cement-based materials with slag at low content presented high free nitrite ion concentration, but the addition of low content of fly ash harmed the corrosion inhibition effect of nitrites. The specimens incorporated with both fly ash and slag can reach the highest free nitrite ion concentration when the compounding proportion was 1:1. It was concluded that the extent of mineral admixtures of the corrosion inhibition effect of nitrites was affected by its type and content.

Unusual Microstructural Development upon Gaseous Nitriding of Fe-4.65at% Al Alloy

2010 ◽  
Vol 89-91 ◽  
pp. 371-376
Author(s):  
S. Meka ◽  
R.E. Schacherl ◽  
E. Bischoff ◽  
Eric J. Mittemeijer
Keyword(s):  
Electron Backscatter Diffraction ◽  
Ferrite Matrix ◽  
Microstructural Development ◽  
Al Alloy ◽  
X Ray Diffraction ◽  
Gaseous Nitriding ◽  
Backscatter Diffraction ◽  
Micro Analysis ◽  
Very High ◽  
Plate Type

Employing NH3/H2 gas mixtures, Fe-4.65at% Al alloy specimens were nitrided to assess how the presence of Al, originally dissolved in the ferrite matrix, influences the development of γ-Fe4N1-x phase in the surface adjacent region. The nitrided specimens were characterized by light microscopy, X-ray diffraction, Electron Backscatter Diffraction and Electron Probe Micro Analysis. Surprisingly, formation of ε-Fe2N1-x was observed, although, for the applied nitriding parameters (nitriding potential and temperature), only the formation of γ-Fe4N1-x would be expected in case of nitriding pure ferrite. An unusual plate-type morphology of γ-Fe4N1-x was observed, contrasting with the usual continuous layer-type growth observed upon nitriding iron, Fe-Cr and Fe-V alloys. These unexpected phenomena may be explained as consequences of the need to realize a very high nitrogen supersaturation in the ferrite matrix in order to initiate the precipitation of AlN.

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