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91.
Artur?P.?DeditiusEmail author Martin?Reich Adam?C.?Simon Alexandra?Suvorova Jaayke?Knipping Malcolm?P.?Roberts Sergey?Rubanov Aaron?Dodd Martin?Saunders 《Contributions to Mineralogy and Petrology》2018,173(6):46
Magnetite from hydrothermal ore deposits can contain up to tens of thousands of parts per million (ppm) of elements such as Ti, Si, V, Al, Ca, Mg, Na, which tend to either structurally incorporate into growth and sector zones or form mineral micro- to nano-sized particles. Here, we report micro- to nano-structural and chemical data of hydrothermal magnetite from the Los Colorados iron oxide–apatite deposit in Chile, where magnetite displays both types of trace element incorporation. Three generations of magnetites (X–Z) were identified with concentrations of minor and trace elements that vary significantly: SiO2, from below detection limit (bdl) to 3.1 wt%; Al2O3, 0.3–2.3 wt%; CaO, bdl–0.9 wt%; MgO, 0.02–2.5 wt%; TiO2, 0.1–0.4 wt%; MnO, 0.04–0.2 wt%; Na2O, bdl–0.4 wt%; and K2O, bdl–0.4 wt%. An exception is V2O3, which is remarkably constant, ranging from 0.3 to 0.4 wt%. Six types of crystalline nanoparticles (NPs) were identified by means of transmission electron microscopy in the trace element-rich zones, which are each a few micrometres wide: (1) diopside, (2) clinoenstatite; (3) amphibole, (4) mica, (5) ulvöspinel, and (6) Ti-rich magnetite. In addition, Al-rich nanodomains, which contain 2–3 wt% of Al, occur within a single crystal of magnetite. The accumulation of NPs in the trace element-rich zones suggest that they form owing to supersaturation from a hydrothermal fluid, followed by entrapment during continuous growth of the magnetite surface. It is also concluded that mineral NPs promote exsolution of new phases from the mineral host, otherwise preserved as structurally bound trace elements. The presence of abundant mineral NPs in magnetite points to a complex incorporation of trace elements during growth, and provides a cautionary note on the interpretation of micron-scale chemical data of magnetite. 相似文献
92.
Yevgeny?A.?GolubevEmail author Olga?V.?Martirosyan 《Physics and Chemistry of Minerals》2012,39(3):247-258
Molecular and supermolecular structures of fossilized resins from the North Eurasia have been studied in detail by IR-spectroscopy,
atomic force microscopy (AFM), scanning (SEM), and high-resolution transmission electron (HRTEM) microscopy. The analysis
of the IR-spectroscopy data allowed to identify the types of the fossil resins (succinite, rumanite, retinite, etc.). In the
succinites and rumanite, the supermolecular structure was observed by AFM. Sizes of the supermolecular particles are 50–120 nm.
Some chain-like and cluster-like aggregates can be observed when globules contact with each other. Using SEM and HRTEM techniques,
it has been shown that mineral impurities are mainly located as scattered inclusions (from one nanometers up to several tens
micrometers in size) in an amorphous organic matrix of the resin. 相似文献
93.
Vania Bogorny Chiara Renso Artur Ribeiro de Aquino Fernando de Lucca Siqueira Luis Otavio Alvares 《Transactions in GIS》2014,18(1):66-88
Several works have been proposed in the last few years for raw trajectory data analysis, and some attempts have been made to define trajectories from a more semantic point of view. Semantic trajectory data analysis has received significant attention recently, but the formal definition of semantic trajectory, the set of aspects that should be considered to semantically enrich trajectories and a conceptual data model integrating these aspects from a broad sense is still missing. This article presents a semantic trajectory conceptual data model named CONSTAnT, which defines the most important aspects of semantic trajectories. We believe that this model will be the foundation for the design of semantic trajectory databases, where several aspects that make a trajectory “semantic” are taken into account. The proposed model includes the concepts of semantic subtrajectory, semantic points, geographical places, events, goals, environment and behavior, to create a general concept of semantic trajectory. The proposed model is the result of several years of work by the authors in an effort to add more semantics to raw trajectory data for real applications. Two application examples and different queries show the flexibility of the model for different domains. 相似文献
94.
Low- and high-temperature heat capacities were measured for a series of synthetic high-structural state (K,Ca)-feldspars (Or–An)
using both a relaxation and a differential scanning calorimeter. The data were collected at temperatures between 5 and 800 K
on polycrystalline samples that had been synthesised and characterised in a previous study. Below T = 300 K, Or90An10, and Or80An20 showed excess heat capacities of mixing with maximum values of ~3 J mol−1 K−1. The other members of this binary (An > 20 mol%) had lower excess heat capacity values of up to ~1 J mol−1 K−1. Above T = 300 K, some compositions exhibited negative excess heat capacities of mixing (with maximum values of −2 J mol−1 K−1). The vibrational entropy at 298.15 K for Or90An10 and Or80An20 deviated strongly from the behaviour of a mechanical mixture, with excess entropy values of ~3.5 J mol−1 K−1. More An-rich members had only small excess vibrational entropies at T = 298.15 K. The difference in behaviour between members with An > 20 mol% and those with An ≤ 20 mol% is probably a consequence
of the structural state of the (K,Ca)-feldspars, i.e., (K,Ca)-feldspars with An ≤ 20 mol% have monoclinic symmetry, whereas
those with An > 20 mol% are triclinic. At T = 800 K, the vibrational entropy values were found to scatter around the values expected for a mechanical mixture and, thus,
correspond to a quasi-ideal behaviour. The solvus for the (K,Ca)-feldspar binary was calculated based on the entropy data
from this study in combination with enthalpy and volume of mixing data from a previous study. 相似文献
95.
The heat capacity at constant pressure, C
p, of chlorapatite [Ca5(PO4)3Cl – ClAp], and fluorapatite [Ca5(PO4)3F – FAp], as well as of 12 compositions along the chlorapatite–fluorapatite join have been measured using relaxation calorimetry
[heat capacity option of the physical properties measurement system (PPMS)] and differential scanning calorimetry (DSC) in
the temperature range 5–764 K. The chlor-fluorapatites were synthesized at 1,375–1,220°C from Ca3(PO4)2 using the CaF2–CaCl2 flux method. Most of the chlor-fluorapatite compositions could be measured directly as single crystals using the PPMS such
that they were attached to the sample platform of the calorimeter by a crystal face. However, the crystals were too small
for the crystal face to be polished. In such cases, where the sample coupling was not optimal, an empirical procedure was
developed to smoothly connect the PPMS to the DSC heat capacities around ambient T. The heat capacity of the end-members above 298 K can be represented by the polynomials: C
pClAp = 613.21 − 2,313.90T
−0.5 − 1.87964 × 107
T
−2 + 2.79925 × 109
T
−3 and C
pFAp = 681.24 − 4,621.73 × T
−0.5 − 6.38134 × 106
T
−2 + 7.38088 × 108
T
−3 (units, J mol−1 K−1). Their standard third-law entropy, derived from the low-temperature heat capacity measurements, is S° = 400.6 ± 1.6 J mol−1 K−1 for chlorapatite and S° = 383.2 ± 1.5 J mol−1 K−1 for fluorapatite. Positive excess heat capacities of mixing, ΔC
pex, occur in the chlorapatite–fluorapatite solid solution around 80 K (and to a lesser degree at 200 K) and are asymmetrically
distributed over the join reaching a maximum of 1.3 ± 0.3 J mol−1 K−1 for F-rich compositions. They are significant at these conditions exceeding the 2σ-uncertainty of the data. The excess entropy of mixing, ΔS
ex, at 298 K reaches positive values of 3–4 J mol−1 K−1 in the F-rich portion of the binary, is, however, not significantly different from zero across the join within its 2σ-uncertainty. 相似文献
96.
A ternary feldspar-mixing model based on calorimetric data: development and application 总被引:8,自引:0,他引:8
Artur Benisek Edgar Dachs Herbert Kroll 《Contributions to Mineralogy and Petrology》2010,160(3):327-337
A mixing model for high structural state ternary feldspars in the NaAlSi3O8–KAlSi3O8–CaAl2Si2O8 system is presented based exclusively on calorimetric and volumetric measurements. Comparisons with existing mixing models,
which are based on phase-equilibrium experiments, reveal distinct differences. The incorporation of K into Ca-rich plagioclase
and of Ca into K-rich alkali feldspar is more strongly limited by our calorimetry-based model, whereas the stability field
of Na-rich feldspars is broadened. Natural feldspar assemblages from well-studied magmatic and high-grade metamorphic rocks
(i.e. a teschenite sill in Scotland, the Klokken syenogabbro in Greenland, and a granulite-facies metapelite in Sri Lanka)
were used to test the mixing models. It was found that the new model largely eliminates discrepancies between observed and
predicted feldspar compositions that were present in earlier attempts. The reasons for the problems associated with phase-equilibrium
based mixing models are discussed. 相似文献