natural quartz
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2021 ◽  
Vol 174 ◽  
pp. 107238
Author(s):  
Bartłomiej A. Gaweł ◽  
Anna Ulvensøen ◽  
Katarzyna Łukaszuk ◽  
Astrid Marie F. Muggerud ◽  
Andreas Erbe

Author(s):  
Michel Bestmann ◽  
Giorgio Pennacchioni ◽  
Bernhard Grasemann ◽  
Benjamin Huet ◽  
Michael W. M. Jones ◽  
...  
Keyword(s):  

Crystals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1145
Author(s):  
Danyi Zhou ◽  
Taijin Lu ◽  
Huiru Dai ◽  
Jieran Lv ◽  
Shouming Chen ◽  
...  

Regrown quartz crystals consist of the natural section and the synthetic section grown by hydrothermal technique, which has become popular on the Chinese jewelry market in recent years. Similar gemological properties to those of natural quartz have brought challenges to gem identification and also new questions to scientific research. In this study, microstructure and spectral characteristics of the two sections of regrown quartz crystals were investigated by three dimensional computed tomography system and infrared spectroscopy. Results showed that the natural section has a higher porosity and there are also many micron- to millimeter-sized pores on the interface of the two sections. Different infrared absorption peaks of the two sections at the 3300–3600 cm−1 range were mainly attributed to the different existence state of OH groups. The distinction of microstructure and spectral characteristics between the natural and synthetic sections indicate their different growth condition. Compared with natural quartz, a relatively stable growth environment during the synthetic process leads to a lower porosity and the alkali growth solution could result in the change of the existence state of OH groups in the regrown quartz crystals.


Geology ◽  
2021 ◽  
Author(s):  
Andreas Audétat ◽  
Nobuyoshi Miyajima ◽  
Dorothea Wiesner ◽  
Jean-Nicolas Audinot

Titanium diffusion profiles in natural quartz crystals have become an increasingly popular tool to reconstruct the time scales of various magmatic, metamorphic, and hydrothermal processes. However, the original calibration of Ti diffusion rates in quartz has recently been challenged, and diffusivities were found to be about three orders of magnitude lower. We performed annealing experiments on crystal-crystal diffusion couples consisting of Ti-free synthetic quartz seeds over which Ti-rich quartz (100–3000 μg/g Ti) was grown hydrothermally. The annealing experiments were performed at 1000–1600 °C and 0.1 MPa to 2.0 GPa, and they lasted for 3–84 days. The resulting diffusion profiles were mapped by cathodoluminescence (CL), transmission electron microscope–energy-dispersive X-ray spectroscopy (TEM-EDXS), and, for the first time, by helium ion microscope–secondary ion mass spectrometry (HIM-SIMS). Obtained diffusion coefficients range from values similar to the lower range in previous research to values up to two orders of magnitude lower. In addition, inversely zoned quartz and sanidine phenocrysts in a natural rhyolite were studied. Comparison of the diffusion profiles suggests that at ~735 °C, the Ti diffusivity in quartz is ~1.5 and 3.0 orders of magnitude lower than that of Ba and Sr, respectively, in sanidine. The combined evidence confirms that Ti diffusion in quartz is very slow, potentially even slower than proposed earlier. Consequently, previous time scales derived from Ti diffusion profiles in quartz are likely orders of magnitude too short, and further experiments are necessary to fully clarify the issue.


2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Shin Toyoda ◽  
Mana Amimoto

Abstract The E1’ centre is one of the most common paramagnetic defects observed by electron spin resonance (ESR) in natural quartz, the formation of which is, however, quite complicated. The dose response to gamma ray irradiation of the E1’ centre in natural quartz was systematically investigated in the present study to find that its dose response depends on the heating conditions of the sample before irradiation. The signal intensity decreases on irradiation when quartz has been heated up to 300°C, while it increases when heated above 400°C. The phenomena can be explained by the electronic processes that heating supplies electronic holes to the oxygen vacancies while gamma ray irradiation supplies electrons.


2021 ◽  
Author(s):  
Alida Timar-Gabor ◽  
Aditi Dave ◽  
Zuzanna Kabacińska ◽  
Kathryn Fitzsimmons

<p>The sediment-routing concept [1] aims to integrate tectonic fluxes and climatically driven erosion, an approach that is at the core of modern studies into Earth-surface processes. The concept relies on the potential to track individual mineral grains from source to sink. Provenance studies are instrumental in this respect; until recently, almost all of these have focussed on accessory minerals. By contrast, the durability and abundance of quartz ensures that parent rocks containing quartz are represented by detrital quartz in their daughter sediment. Even the purest quartz crystal contains a vast number of point defects, which may be either intrinsic or due to impurities. Some of these defects remain unchanged under ionising radiation bombardment by natural environmental radioactivity, while others are transformed, generally in the form of charge trapping. Based on the dynamics of some of these radiation-sensitive defects under irradiation, quartz is frequently used for dating by luminescence or electron spin resonance (ESR). Another, less explored, application of these defects is the fingerprinting of sediment sources. For provenance applications to be successful, sedimentary quartz signals used should match the corresponding signals of quartz from the host rocks: they should remain unchanged during transport and/or weathering processes.</p><p>Here we conduct an exploratory study on fine (4-11 μm) quartz from loess from Central Asia (Kazakhstan and Tajikistan), a region dominated by westerly air transport. These study sites were chosen since recent studies based on geochemical fingerprinting, grain-size modelling and meteorological reanalysis suggest the contribution from different source areas [2,3]. We investigate the signature of E’ (≡Si·, an unpaired electron at an oxygen vacancy site) and peroxy intrinsic defect centers (≡Si-O-O·and ≡Si–O· non-bridging oxygen) using ESR, by measuring both quartz grains extracted from both untreated samples, and from samples irradiated to 2000 Gy and subsequently heated to 10 min at 350 °C (as suggested by Toyoda and others [4]). By investigating the dose response of these signals, with and without the application of thermal treatments, we conclude that natural E` signals hold great promise for provenance studies, thus considerably simplifying the currently used measurement protocols. We observe a significant difference between the E’ and peroxy signals between the Kazakh and Tajik samples, which is in tune with the hypothesis that the two loess sites derive from different dust sources.</p><p>References</p><p>1. Allen, P.A., 2008. From landscapes into geological history. Nature 451, 274-276.</p><p>2. Li, Y., Song, Y., Fitzsimmons, K., Chen, X., Wang, Q., Sun, H., Zhang, Z., 2018. New evidence for the provenance and formation of loess deposits in the Ili river basin, Arid Central Asia. Aeolian Research 35, 1-8.</p><p>3. Li, Y., Song, Y., Kaskaoutis, D.G., Chen, X., Mamadjanov, Y., Tan, L., 2019. Atmospheric dust dynamics in southern Central Asia: Implications for buildup of Tajikistan loess sediments. Atmospheric Research 229, 74-85.</p><p>4. Toyoda, S., 2011. The E<sub>1</sub>` centre in natural quartz: its formation and applications to dating and provenance reserarches. Geochronometria, 38 (3), 242-248.</p>


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