1,721,017 research outputs found
The origin and significance of euhedral apatite crystals on conodonts
Full text linkCrystal overgrowth on fossil remains is well-documented in the literature. Attention has specifically focused on
bioapatite (i.e., an apatite of biochemical origin regardless of post-mortem changes) configurations, in order to
decipher any possible relation to fossilization/diagenesis. This study investigates the Rare Earth Element (REE)
and other High-Field-Strength Element (HFSE) composition of euhedral crystals formed on the surface of conodont elements compared with that of crystal-free surfaces. Euhedral crystals are by definition crystals characterized by sharp faces, developing solids that, for apatite, assume the form of hexagonal prisms, reflecting its crystal symmetry. Late Ordovician (Amorphognathus ordovicicus Zone) conodonts from two localities in Sardinia and the Carnic Alps (Italy) are herein investigated. Conodont elements reveal the occurrence of smooth surfaces and surfaces partially covered with euhedral crystals. Since euhedral crystals did not reasonably grow during the organism’s lifetime, the REE and HFSE analysis can provide important insights into the crystal growth process. The experimental results indicated a substantial contribution of diagenetic imprinting for all the analyzed material, although more evident on euhedral crystals that are significantly enriched in middle and, subordinately, in heavy REE with respect to smooth surfaces. The positive correlations between La + Th vs log[ΣREE] and Ce + Th
vs log[ΣREE] could support the hypothesis that the neoformed euhedral crystals grew also by depleting the pristine bioapatite of the conodont elements. Nevertheless, the occurrence of two types of apatite cannot be ruled out: euhedral crystals as neoformed products of diagenetic processes and smooth surfaces as remains of the pristine conodont bioapatite after diagenesis
CRYSTALLOGRAPHIC FEATURES AND CLEAVAGE NANOMORPHOLOGY OF CHLINOCHLORE: SPECIFIC APPLICATIONS
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A multidisciplinary approach in recognizing seep-carbonates: A case study from the Loiano Formation (late Eocene) in the northern Apennines (Italy)
No full textStructure and mineralogy of layer silicates: recent perspectives and new trends
No full textBecause of their many novel and advanced applications, there is increasing interest in layer silicates from the scientific and technical communities. Appropriate application of these minerals requires deep understanding of their properties and of the processes where they are involved. This chapter, by providing fundamental definitions and crystal structural and chemical data pertaining to layer silicates, aims to introduce this field to new researchers and technicians, by describing the fundamental features leading to different behaviours of layer silicates in different natural or technical processes. The subject addressed is vast and so the reader is referred in some cases to work already published. The focus here is on layer silicates for which detailed crystal structures are given in the literature and which are likely to be used in an applied way in the future. Layer-silicate minerals fulfilling these requirements are: (1) kaolin-serpentine group (e. g. kaolinite, dickite, nacrite, halloysite, hisingerite, odinite, lizardite, berthierine, amesite, cronstedtite, nepouite, kellyite, fraipontite, brindleyite, guidottiite, bementite, greenalite, caryopilite; minerals of the pyrosmalite series); (2) talc and pyrophyllite groups (e. g. pyrophyllite, ferripyrophyllite, willemseite); (3) mica group (i.e. some recent advances in crystal chemistry and structure of dioctahedral and trioctahedral micas); (4) smectite group (e. g. montmorillonite, saponite, hectorite, sauconite, stevensite, swinefordite); (5) vermiculite group; (6) chlorite group (e. g. trioctahedral chlorite such as clinochlore, di,trioctahedral and dioctahedral chlorites such as cookeite and sudoite); (7) some 2: 1 layer silicates involving a discontinuous octahedral sheet and a modulated tetrahedral sheet such as kalifersite, palygorskite and sepiolite; and (8) imogolite and allophane
The Oligocene-Miocene volcanism in the Apennine: discovery and characterization of baryte and phillipsite-Ba rich bed in the lower part of the Ranzano Formation (Reggio Emilia, Italy)
No full textThis work reports the biostratigraphic assessment and the
chemical and mineralogical characterization of a zeolitized and
barium-rich volcanic pyroclastic bed outcropping in the lower Secchia
Valley (Northern Apennines, Italy), very close to the boundary between
the Ranzano and the Monte Piano Formations. To our knowledge, it
is the older so far documented in the Emilian Epiligurian Succession
as, through nannofossil biostratigraphy, we have documented an early
Oligocene age (Rupelian CNO1 nannofossil zone) for the enclosing
sediments. The chemical and mineralogical composition, the latter
obtained through a multi-analytical approach combining X-ray powder
diffraction (Rietveld-RIR method) with thermal analyses coupled
with evolved gas mass spectrometry, revealed large amounts of Barich phillipsite, baryte, volcanic glass and subordinate quantities of
sanidine and plagioclase; on the other hand, phlogopite, idiomorphic
plagioclase and femic minerals, frequently found in younger volcanic
layers of the Ranzano Formation, here are absent. The quantitative
mineralogical assessment together with mineral associations suggest
that diagenesis did not play a relevant role in the crystallization of
phillipsite, but its role cannot be neglected for the crystallization of
baryte. Hypothesis on the genesis and transformation of the original
material and on the possible correlation with the coeval calc-alkaline
magmatic sources in the circum-Mediterranean area were considered,
but no definitive conclusion has been reached
Response to Tilic and Bartolomaeus's Commentary on the original Research Paper “Unravelling the ultrastructure and mineralogical composition of fireworm stinging bristles” (Zoology, 144)
No full textIn their Commentary to our paper recently published in Zoology (Righi et al., 2021a), Tilic and Bartolomaeus question our findings that the chaetae of Hermodice carunculata (Annelida) are hollow and able to store and deliver venoms. They sustain the idea that inflammatory chemicals are secreted through epidermal glands and possibly exposed to predator trough wounds caused by the brittle chaetae. We provide evidence-based arguments in support of our considerations. The sample preparation procedures did not affect the native inner structure of unfixed fireworm chaetae, which is clearly hollow as supported by both ultrastructure observation and crystal-chemical analysis of constituents. Furthermore, our previous and more recent feeding bioassays and chemical analysis indicate both that chaetae retain strong deterrent capacities even when isolated from the body of H. carunculata, and that they contain venoms. The cellular mechanisms involved in fireworm chaeta storage and deliver of chemicals are still unstudied. We strongly believe that this lack of knowledge should draw further attention on H. carunculata biology, pursuing new hypotheses and studies based on the noteworthy information which has been obtained so far
To be or not to be a conodont. The controversial story of Pseudooneotodus and Eurytholia
Full text linkThe genus Pseudooneotodus (Drygant, 1974) is a genus of small and conical elements widely distributed from the Middle Ordovician to the Early Devonian throughout the world. Because of its unusual shape, Pseudooneotodus has long been considered enigmatic, and only in the late nineties of the last century the genus has been finally placed within conodonts according to histological data. This study investigates possible similarities between Pseudooneotodus and Eurytholia (Sutton et al., 2001), an incertae sedis genus of enigmatic plates with a phosphate composition. An association of over one hundred specimens of Pseudooneotodus beckmanni and Eurytholia bohemica was analyzed from conodont residues in two distinct geographical areas: the Prague Basin (Požáry and Mušlovka sections, Bohemia, Czech Republic) and the Carnic Alps (Rauchkofel Boden section, Austria). Through an investigation that combines the use of optical and electron microscopy (including focused ion beam scanning electron microscopy), X-ray microdiffraction, and trace element (HFSE) analysis by mass spectrometry, differences between these fossil groups were observed and compared with data resulting from typical conodonts (Dapsilodus obliquicostatus, Panderodus unicostatus and Wurmiella excavata) recovered from the same samples
Optimizing Hempcrete Properties Through Thermal Treatment of Hemp Hurds for Enhanced Sustainability in Green Building
Full text linkThis study examines the effects of the thermal pre-treatment of hemp hurds on the physical, mechanical, and thermal properties of hempcrete, evaluating its potential as a sustainable building material. Hemp hurds were pre-treated at various temperatures (120–280 °C) and characterized by proximate analysis, CHNS elemental analysis, and thermogravimetric analysis (TGA). The resulting hempcrete samples were analyzed for density, water absorption, compressive strength, and thermal conductivity. Three different hempcrete formulations, with varying lime:hemp proportions, were analyzed. The findings indicate that higher pre-treatment temperatures lead to reduced density and water absorption across all formulations. Formulations containing a higher hemp hurd content had lower densities but higher water absorption values. Compressive strength increased consistently with the pre-treatment temperature, suggesting that higher temperatures enhance matrix bonding and structural rigidity, and with the lime content. However, thermal conductivity also rose with pre-treatment, with only the composition containing the highest hemp hurd content maintaining the optimal insulation threshold (0.1 W/mK). This suggests a trade-off between compressive strength and insulation performance, influenced by the balance of hemp hurd and lime content. These findings underscore the potential of thermal pre-treatment to tailor hempcrete properties, promoting its application as a durable, moisture-resistant material for sustainable building, though the optimization of hurd–lime ratios remains essential
Crystal structure and crystal chemistry of fluorannite and its relationships to annite
No full textWe present the crystal chemical characterization of fluorannite from Katugin Ta-Nb deposit, Chitinskaya Oblast’, Kalar Range, Transbaikalia, Eastern-Siberian Region, Russia. This mica belongs to 1M polytype (space group C2/m) with layer parameters a = 5.3454(2) Å, b = 9.2607(4) Å, c = 10.2040(5) Å, ? = 100.169(3)°. Structure refinement, using anisotropic displacement parameters, converged at R = 0.0384. Fluorannite shows a smaller cell volume (V = 497.19 Å3) than annite (V = 505.71 Å3) because of its smaller lateral dimensions and its reduced c parameter. The flattening of the tetrahedral basal oxygen atoms plane decreases with F content, together with the A-O4 distance (i.e., the distance between interlayer A cation and the octahedral anionic position) because of the reduced repulsion between the interlayer cation and the anion sited in O4
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