scholarly journals Mineral composition of host sediments influences the fossilization of soft tissues

2018 ◽  
Vol 55 (11) ◽  
pp. 1271-1283 ◽  
Author(s):  
Elena Naimark ◽  
Maria Kalinina ◽  
Alexander Shokurov ◽  
Alexander Markov ◽  
Liubov Zaytseva ◽  
...  
Keyword(s):  
Soft Tissues ◽  
Mineralogical Composition ◽  
Artemia Salina ◽  
New Mineral ◽  
X Ray ◽  
Mineral Phases ◽  
Long Term Experiments ◽  
Host Rocks

Cambrian Lagerstätten host rocks are frequently composed of kaolinite and chlorite in varying amounts; accordingly, our goal was to study the preservation potential of crustaceans in these two clays. We conducted long-term experiments (12–18 months, the longest duration of actualistic taphonomy experiments from published literature) on the decay of Artemia salina in these clay sediments. The degree of preservation, transformed mineralogical composition of the sediments, and the elemental composition of the nauplial remains were examined. We demonstrate that the kaolinite and chlorite sediment enhanced the preservation (in the kaolinite the effect was considerably higher than in the chlorite) compared with the sediment-free control. pH inside the sediments dropped to 6.5–7.1 and was even lower (<4) around the buried carcasses, facilitating the dissolution of clays. This phenomenon was confirmed by mineralogical analyses of the experimental sediments, which showed mineralogical signatures of such dissolution and new mineral phases. According to the variations in the dissolved minerals in the sediments, different cations entered the buried remains as was shown by the multiple energy dispersive X-ray analyses. An increased level of Mg was detected in the carcasses buried in chlorite, whereas Al and Si concentrations were higher in the kaolinite; in both cases, Ca rapidly entered the decaying tissues from marine water. Bacteria underwent similar mineralization as the macroremains and apparently had no direct effect on the mineralization. The results confirmed an important role of dissolved Al ions in preservation of soft-bodied organisms in clay-dominated sediments and explained wide variation in chemical composition of their fossils.

SEM-based mineralogical mapping at the submicrometer-scale of modern Sardinian stromatolites

2021 ◽  
Author(s):  
Juliette Debrie ◽  
Dimitri Prêt ◽  
Karim Benzerara ◽  
Jean Paul Saint Martin
Keyword(s):  
Mineralogical Composition ◽  
Treatment Method ◽  
Heterogeneous Distribution ◽  
X Ray ◽  
Mineral Phases ◽  
Saint Martin ◽  
History Of ◽  
Phase Recognition ◽  
Mineral Mixtures ◽  
Insight Into

&lt;p&gt;Stromatolites, i.e. macroscopically laminated carbonate rocks formed by diverse microbial communities, are particularly emblematic geobiological materials since they are the oldest evidence of life-mineral interactions, dated up to 3.5 Gyrs ago. &amp;#160;They are found throughout the history of the Earth and have received strong attention because they provide precious information about microbial paleobiodiversity and paleoenvironments. However, while this information is interpreted based on our knowledge about modern analogs, the latter remains very incomplete. Here, we studied recently discovered modern stromatolites from Mari Ermi&lt;sup&gt;1&lt;/sup&gt;, a coastal pond in Western Sardinia, that seasonally experience severe evaporation and broad salinity variations. For this purpose, we explored the mineralogical composition of these unique sedimentary archives and its spatial variations in order to gain better insight into how mineral phases record the conditions and processes of their formation. We investigated the heterogeneous distribution of minerals using quantitative X-ray chemical maps provided by energy dispersive x-ray spectrometry analyses coupled with scanning electron microscopy (SEM-EDXS). Hyperspectral maps were analyzed using an innovative data treatment method &lt;sup&gt;2&lt;/sup&gt; allowing phase recognition within the complex mineral mixtures and solid solutions encountered. This method provided quantitative data on&amp;#160;spatial distribution, modal content and associated calculated unit formulas for each identified mineral and phase with a hundred nanometer resolution. Based on these results, we will discuss the origin of the laminations in the stromatolites.&lt;/p&gt;&lt;p&gt;Reference:&lt;/p&gt;&lt;p&gt;1. Saint Martin, J.-P. &amp; Saint Martin, S. Geo-Eco-Marina &lt;strong&gt;21&lt;/strong&gt;, 35&amp;#8211;53 (2015a).&lt;/p&gt;&lt;p&gt;2. Pr&amp;#234;t, D. et al. American Mineralogist &lt;strong&gt;95&lt;/strong&gt;, 1379&amp;#8211;1388 (2010).&lt;/p&gt;

scholarly journals Radiation damage from long-term alpha particle bombardment of silicates – a microfocus XRD and Fe K-edge XANES study

2015 ◽  
Vol 79 (6) ◽  
pp. 1455-1466 ◽  
Author(s):  
W. R. Bower ◽  
C. I. Pearce ◽  
G. T. R. Droop ◽  
J. F. W. Mosselmans ◽  
K. Geraki ◽  
...  
Keyword(s):  
Radiation Damage ◽  
Ion Irradiation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Radiation Fields ◽  
Mineral Phases ◽  
Particle Damage ◽  
X Ray Absorption ◽  
Defect Densities

AbstractA detailed understanding of the response of mineral phases to the radiation fields experienced in a geological disposal facility (GDF) is currently poorly constrained. Prolongued ion irradiation has the potential to affect both the physical integrity and oxidation state of materials and therefore may alter a structure's ability to react with radionuclides. Radiohalos (spheres of radiation damage in minerals surrounding radioactive (α-emitting) inclusions) provide useful analogues for studying long term α-particle damage accumulation. In this study, silicate minerals adjacent to Th- and U-rich monazite and zircon were probed for redox changes and long/short range disorder using microfocus X-ray absorption spectroscopy (XAS) and high resolution X-ray diffraction (XRD) at Beamline I18, Diamond Light Source. Fe3+ → Fe2+ reduction has been demonstrated in an amphibole sample containing structural OH– groups – a trend not observed in anhydrous phases such as garnet. Coincident with the findings of Pattrick et al. (2013), the radiolytic breakdown of OH– groups is postulated to liberate Fe3+ reducing electrons. Across all samples, high point defect densities and minor lattice aberrations are apparent adjacent to the radioactive inclusion, demonstrated by micro-XRD.

Micromorphology and Mineralogy of Fly Ash and Lime Stabilized Bentonite

1987 ◽  
Vol 113 ◽  
Author(s):  
Ray E. Ferrell ◽  
Ara Arman ◽  
Gokhan Baykal
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Unconfined Compressive Strength ◽  
Calcium Silicate Hydrate ◽  
New Mineral ◽  
X Ray ◽  
Mineral Phases ◽  
Clay Aggregates ◽  
Montmorillonitic Clay

ABSTRACTCompacted fly ash, lime, bentonite and water mixtures were cured at 23° and 50°C, for 1, 28, 90 and 180 days. Cementitious products and microstructure were observed by scanning electron microscopy, energy dispersive x-ray spectrometry and x-ray diffractometry. Unconfined compressive strength changes are correlated to the formation of new mineral phases. For bentonite-limefly ash mixtures, strength increased from 1050 kPa (I day) to 2,300 kPa (90 days) and then slightly increased to 2,400 kPa after 180 days at ∼ 230C. Ettringite is the most abundant mineral associated with the increased compressive strength.New minerals identified in the 23°C mixtures include calcium silicate hydrate - Type 1, afwillite and ettringite. Acicular crystals of these and other minerals were formed by the hydration of lime and fly ash in the montmorillonitic clay. The cementitious phases create a rigid framework joining spheres and clay aggregates. Continued reaction dissolves some of the spheres and slightly reduces the rigidity of the cured samples.

scholarly journals Cold fronts: probes of plasma astrophysics in galaxy clusters

2016 ◽  
Vol 82 (3) ◽  
Author(s):  
John A. ZuHone ◽  
E. Roediger
Keyword(s):  
Galaxy Clusters ◽  
Mean Free Path ◽  
Magnetized Plasma ◽  
X Ray ◽  
Gas Phases ◽  
Cold Fronts ◽  
The Mean ◽  
The Stability

The most massive baryonic component of galaxy clusters is the ‘intracluster medium’ (ICM), a diffuse, hot, weakly magnetized plasma that is most easily observed in the X-ray band. Despite being observed for decades, the macroscopic transport properties of the ICM are still not well constrained. A path to determine macroscopic ICM properties opened up with the discovery of ‘cold fronts’. These were observed as sharp discontinuities in surface brightness and temperature in the ICM, with the property that the denser side of the discontinuity is the colder one. The high spatial resolution of the Chandra X-ray Observatory revealed two puzzles about cold fronts. First, they should be subject to Kelvin–Helmholtz instabilities, yet in many cases they appear relatively smooth and undisturbed. Second, the width of the interface between the two gas phases is typically narrower than the mean free path of the particles in the plasma, indicating negligible thermal conduction. It was thus realized that these special characteristics of cold fronts may be used to probe the properties of the cluster plasma. In this review, we will discuss the recent simulations of cold fronts in galaxy clusters, focusing on those which have attempted to use these features to constrain ICM physics. In particular, we will examine the effects of magnetic fields, viscosity, and thermal conductivity on the stability properties and long-term evolution of cold fronts. We conclude with a discussion on what important questions remain unanswered, and the future role of simulations and the next generation of X-ray observatories.

The Role of Magnesium in Blood Coagulation

1967 ◽  
Vol 18 (03/04) ◽  
pp. 626-633 ◽  
Author(s):  
I Szelényi ◽  
J Rigô ◽  
B. O Ahmed ◽  
J Sos
Keyword(s):  
Blood Coagulation ◽  
Blood Platelets ◽  
Saturated Fat ◽  
Functional Importance ◽  
Long Term Experiments ◽  
Cellular Oxidation ◽  
The One ◽  
Physiological Type

SummaryHypercoagulative tendencies elicited by saturated fat could be repressed by oral or venous administration of magnesium in acute as well as in long term experiments.Magnesium appears to have double functional importance in coagulation : On the one hand, it exerts direct influence by antagonizing calcium, promoting fibrinolysis, and stabilizing fibrinogen and blood platelets and, on the other hand, it acts indirectly as well in that it causes vasodilatation and favours cellular oxidation.In the dynamic equilibrum of the processes taking part in blood coagulation magnesium appears to play its role as a physiological type of anticoagulant.

scholarly journals Wet–dry cycles impact DOM retention in subsurface soils

2018 ◽  
Vol 15 (3) ◽  
pp. 821-832 ◽  
Author(s):  
Yaniv Olshansky ◽  
Robert A. Root ◽  
Jon Chorover
Keyword(s):  
Arid Regions ◽  
Critical Zone ◽  
Mineral Surfaces ◽  
Soil Matrix ◽  
Organic C ◽  
X Ray ◽  
Mineral Phases ◽  
Scanning Transmission ◽  
X Ray Absorption

Abstract. Transport and reactivity of carbon in the critical zone are highly controlled by reactions of dissolved organic matter (DOM) with subsurface soils, including adsorption, transformation and exchange. These reactions are dependent on frequent wet–dry cycles common to the unsaturated zone, particularly in semi-arid regions. To test for an effect of wet–dry cycles on DOM interaction and stabilization in subsoils, samples were collected from subsurface (Bw) horizons of an Entisol and an Alfisol from the Catalina-Jemez Critical Zone Observatory and sequentially reacted (four batch steps) with DOM extracted from the corresponding soil litter layers. Between each reaction step, soils either were allowed to air dry (wet–dry treatment) before introduction of the following DOM solution or were maintained under constant wetness (continually wet treatment). Microbial degradation was the dominant mechanism of DOM loss from solution for the Entisol subsoil, which had higher initial organic C content, whereas sorptive retention predominated in the lower C Alfisol subsoil. For a given soil, bulk dissolved organic C losses from solution were similar across treatments. However, a combination of Fourier transform infrared (FTIR) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopic analyses revealed that wet–dry treatments enhanced the interactions between carboxyl functional groups and soil particle surfaces. Scanning transmission X-ray microscopy (STXM) data suggested that cation bridging by Ca2+ was the primary mechanism for carboxyl association with soil surfaces. STXM data also showed that spatial fractionation of adsorbed OM on soil organo-mineral surfaces was diminished relative to what might be inferred from previously published observations pertaining to DOM fractionation on reaction with specimen mineral phases. This study provides direct evidence of the role of wet–dry cycles in affecting sorption reactions of DOM to a complex soil matrix. In the soil environment, where wet–dry cycles occur at different frequencies from site to site and along the soil profile, different interactions between DOM and soil surfaces are expected and need to be considered for the overall assessment of carbon dynamics.

Study of Ettringite by Hydration of Yeelimite Clinker

2016 ◽  
Vol 865 ◽  
pp. 126-129
Author(s):  
Radek Magrla ◽  
Karel Dvořák ◽  
Dominik Gazdič ◽  
Marcela Fridrichová
Keyword(s):  
Mineralogical Composition ◽  
Raw Material ◽  
Fluidized Bed Combustion ◽  
X Ray Diffraction ◽  
Laboratory Environment ◽  
X Ray ◽  
Ettringite Formation ◽  
Experimental Works ◽  
Potential Use

This article describes the results of experimental works, dealing with long-term observing of ettringite stability (Ca6Al2(SO4)3(OH)12·26H2O). Thermodynamic stability of this mineral is important in terms of potential use of fluidized bed combustion (FBC) ash as an additive to Portland cement. Within the experimental work it was carried out observing of the ettringite formation by hydration of yeelimitu (Ca4Al6(SO4)·O12) in laboratory conditions. For the preparation of yeelimite it was proposed a three-component raw material mixture, consisting of a high percent limestone and gypsum and corundum. This mixture was subsequently placed in platinum crucibles and burnt in superkanthal kiln at 1200 °C. Formed clinker was mixed in chosen ratio with water and it was prepared a set of testing samples. These samples were exposed in the laboratory environment for up to 180 days. The hydration of the clinker was carried out using X-ray diffraction analysis (XRD) by determining the mineralogical composition.

scholarly journals MINERALOGICAL AND CHEMICAL COMPOSITION OF CFB FLY ASH DERIVED FROM CO-COMBUSTION OF XYLITE AND BIOMASS

2007 ◽  
Vol 40 (2) ◽  
pp. 859
Author(s):  
N. Koukouzas ◽  
J. Hämäläinen ◽  
D. Papanikolaou ◽  
A. Tourunen ◽  
T. Jäntti
Keyword(s):  
Fly Ash ◽  
Mineralogical Composition ◽  
Fluidised Bed ◽  
Chemical Analyses ◽  
X Ray Diffraction ◽  
Mineral Phase ◽  
X Ray ◽  
Mineral Phases ◽  
Circulating Fluidised Bed ◽  
Different Parts

The chemical and mineralogical composition of fly ash samples collected from different parts of two Circulating Fluidised Bed (CFB) facilities has been investigated. The fuels used, were Greek xylite/suhbituminous coal (from the Fiorina basin), Polish coal (from the Catowice region - Poland) and wood chips (Swedish conifer). The characterisation of the fly ash samples included chemical analyses, particle size distribution and X-ray diffraction. According to the chemical analyses the produced fly ashes are rich in CaO. Moreover, S1O2 is the dominant oxide in fly ash with Al203 and Fe2Oi found in considerable quantities. Finally, results obtained by XRD showed that the major mineral phase of fly ash is quartz, while other mineral phases that are occurred are maghemite, hematite, periclase, rutile, gehlenite and anhydrite, while the aforementioned mineral phases were identified by scanning electron microscope (SEM).

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