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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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21 pages, 6549 KiB  
Article
Metal Sequestration through Coupled Dissolution–Precipitation at the Brucite–Water Interface
by Jörn Hövelmann, Christine V. Putnis and Liane G. Benning
Minerals 2018, 8(8), 346; https://doi.org/10.3390/min8080346 - 10 Aug 2018
Cited by 28 | Viewed by 6752
Abstract
The increasing release of potentially toxic metals from industrial processes can lead to highly elevated concentrations of these metals in soil, and ground- and surface-waters. Today, metal pollution is one of the most serious environmental problems and thus, the development of effective remediation [...] Read more.
The increasing release of potentially toxic metals from industrial processes can lead to highly elevated concentrations of these metals in soil, and ground- and surface-waters. Today, metal pollution is one of the most serious environmental problems and thus, the development of effective remediation strategies is of paramount importance. In this context, it is critical to understand how dissolved metals interact with mineral surfaces in soil–water environments. Here, we assessed the processes that govern the interactions between six common metals (Zn, Cd, Co, Ni, Cu, and Pb) with natural brucite (Mg(OH)2) surfaces. Using atomic force microscopy and a flow-through cell, we followed the coupled process of brucite dissolution and subsequent nucleation and growth of various metal bearing precipitates at a nanometer scale. Scanning electron microscopy and Raman spectroscopy allowed for the identification of the precipitates as metal hydroxide phases. Our observations and thermodynamic calculations indicate that this coupled dissolution–precipitation process is governed by a fluid boundary layer at the brucite–water interface. Importantly, this layer differs in composition and pH from the bulk solution. These results contribute to an improved mechanistic understanding of sorption reactions at mineral surfaces that control the mobility and fate of toxic metals in the environment. Full article
(This article belongs to the Special Issue Mineral Surface Reactions at the Nanoscale)
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16 pages, 3707 KiB  
Article
The Influence of Spectral Interferences on Critical Element Determination with Portable X-Ray Fluorescence (pXRF)
by Daniela Gallhofer and Bernd G. Lottermoser
Minerals 2018, 8(8), 320; https://doi.org/10.3390/min8080320 - 27 Jul 2018
Cited by 56 | Viewed by 9861
Abstract
Field portable X-ray fluorescence (pXRF) spectrometers are routinely used in mineral resources studies. To date, mineral resources studies have largely focussed on the application of pXRF to the exploration for deposits of base and precious metals. By contrast, studies using pXRF for the [...] Read more.
Field portable X-ray fluorescence (pXRF) spectrometers are routinely used in mineral resources studies. To date, mineral resources studies have largely focussed on the application of pXRF to the exploration for deposits of base and precious metals. By contrast, studies using pXRF for the quantification of critical elements in geological materials are scarce since these elements are difficult to determine with energy-dispersive pXRF technology. This study explores the capability of pXRF spectrometers to detect and quantify critical elements (Ba, P, Nb, V, Co, REE, W, Bi, Hf, and Ta) in certified reference materials (CRMs). While precision of many critical elements is acceptable (<20% RSD), accuracy can be poor (>50% difference) when using pre-installed factory calibration software. Spectra collected during the pXRF measurements show that poor accuracy and false positives tend to be associated with spectral interferences. Distinct combinations of spectral interferences (line overlaps, Compton scattered peaks, and Si escape peaks) were observed in the different matrix types. Our results show that critical elements may be determined in common geological materials when pronounced peaks occur in the spectra and that matrix-match of standards and samples is essential. Hence, XRF spectra should be routinely reviewed to identify erroneous quantification due to spectral interferences. Full article
(This article belongs to the Special Issue Selected Papers from the 1st International Conference – Mines of the Future)
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16 pages, 548 KiB  
Article
What the Diffuse Layer (DL) Reveals in Non-Linear SFG Spectroscopy
by Simone Pezzotti, Daria Ruth Galimberti, Y. Ron Shen and Marie-Pierre Gaigeot
Minerals 2018, 8(7), 305; https://doi.org/10.3390/min8070305 - 20 Jul 2018
Cited by 33 | Viewed by 5280
Abstract
Following our recent work [Phys. Chem. Chem. Phys. 20:5190–99 (2018)] that provided the means to unambigously define and extract the three water regions at any charged interface (solid–liquid and air–liquid alike), denoted the BIL (Binding Interfacial Layer), DL (Diffuse Layer) and Bulk, and [...] Read more.
Following our recent work [Phys. Chem. Chem. Phys. 20:5190–99 (2018)] that provided the means to unambigously define and extract the three water regions at any charged interface (solid–liquid and air–liquid alike), denoted the BIL (Binding Interfacial Layer), DL (Diffuse Layer) and Bulk, and how to calculate their associated non-linear Sum Frequency Generation Spectroscopy (SFG) χ2(ω) spectroscopic contributions from Density Functional Theory (DFT)-based ab initio molecular dynamics simulations (DFT-MD/AIMD), we show here that the χDL2(ω) signal arising from the DL water region carries a wealth of essential information on the microscopic and macroscopic properties of interfaces. We show that the χDL2(ω) signal carries information on the surface potential and surface charge, the isoelectric point, EDL (Electric Double Layer) formation, and the relationship between a nominal electrolyte solution pH and surface hydroxylation state. This work is based on DFT-MD/AIMD simulations on a (0001) α–quartz–water interface and on the air–water interface, with various surface quartz hydroxylation states and various electrolyte concentrations. The conclusions drawn make use of the interplay between experiments and simulations. Most of the properties listed above can now be extracted from experimental χDL2(ω) alone with the protocols given in this work, or by making use of the interplay between experiments and simulations, as described in this work. Full article
(This article belongs to the Special Issue Molecular Simulation of Mineral-Solution Interfaces)
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17 pages, 4332 KiB  
Article
Insights into Extinct Seafloor Massive Sulfide Mounds at the TAG, Mid-Atlantic Ridge
by Berit Lehrmann, Iain J. Stobbs, Paul A.J. Lusty and Bramley J. Murton
Minerals 2018, 8(7), 302; https://doi.org/10.3390/min8070302 - 18 Jul 2018
Cited by 16 | Viewed by 7255
Abstract
Over the last decade there has been an increasing interest in deep-sea mineral resources that may contribute to future raw metal supply. However, before seafloor massive sulfides (SMS) can be considered as a resource, alteration and weathering processes that may affect their metal [...] Read more.
Over the last decade there has been an increasing interest in deep-sea mineral resources that may contribute to future raw metal supply. However, before seafloor massive sulfides (SMS) can be considered as a resource, alteration and weathering processes that may affect their metal tenor have to be fully understood. This knowledge cannot be obtained by assessing the surface exposures alone. Seafloor drilling is required to gain information about the third dimension. In 2016, three extinct seafloor massive sulfide mounds, located in the Trans-Atlantic Geotraverse (TAG) hydrothermal area of the Mid-Atlantic Ridge were drilled. A mineralogical and textural comparison of drill core and surface-grab samples revealed that in recent ceased mounds high-temperature copper assemblages typical for black smoker chimneys are still present whereas in longer extinct mounds the mineralogy is pre-dominated by an iron mineral assemblage. Zinc becomes remobilized early in the mound evolution and forms either a layer in the upper part of the mound or has been totally leached from its interior. Precipitation temperatures of sphalerite calculated using the Fe/Zn ratio can help to identify these remobilization processes. While the Fe/Zn ratios of primary sphalerites yield temperatures that are in very good agreement with fluid temperatures measured in white smokers, calculated temperatures for sphalerites affected by remobilization are too high for SMS. Overall drilling of SMS provides valuable information on the internal structure and mineralogy of the shallow sub-surface, however, additional drilling of SMS, at a greater depth, is required to fully understand the processes affecting SMS and their economic potential. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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21 pages, 13097 KiB  
Review
Fly Ash-Based Geopolymer Binder: A Future Construction Material
by Nakshatra B. Singh
Minerals 2018, 8(7), 299; https://doi.org/10.3390/min8070299 - 12 Jul 2018
Cited by 196 | Viewed by 32599
Abstract
A large amount of waste coming out from industries has posed a great challenge in its disposal and effect on the environment. Particularly fly ash, coming out from thermal power plants, which contains aluminosilicate minerals and creates a lot of environmental problems. In [...] Read more.
A large amount of waste coming out from industries has posed a great challenge in its disposal and effect on the environment. Particularly fly ash, coming out from thermal power plants, which contains aluminosilicate minerals and creates a lot of environmental problems. In recent years, it has been found that geopolymer may give solutions to waste problems and environmental issues. Geopolymer is an inorganic polymer first introduced by Davidovits. Geopolymer concrete can be considered as an innovative and alternative material to traditional Portland cement concrete. Use of fly ash as a raw material minimizes the waste production of thermal power plants and protects the environment. Geopolymer concretes have high early strength and resistant to an aggressive atmosphere. Methods of preparation and characterization of fly ash-based geopolymers have been presented in this paper. The properties of geopolymer cement/mortar/concrete under different conditions have been highlighted. Fire resistance properties and 3D printing technology have also been discussed. Full article
(This article belongs to the Special Issue Geopolymers)
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36 pages, 40685 KiB  
Article
High-Resolution Analysis of Critical Minerals and Elements in Fe–Mn Crusts from the Canary Island Seamount Province (Atlantic Ocean)
by Egidio Marino, Francisco Javier González, Rosario Lunar, Jesús Reyes, Teresa Medialdea, Mercedes Castillo-Carrión, Eva Bellido and Luis Somoza
Minerals 2018, 8(7), 285; https://doi.org/10.3390/min8070285 - 2 Jul 2018
Cited by 56 | Viewed by 9188
Abstract
Two Fe–Mn crusts among 35 samples, from six seamounts in the Canary Island Seamount Province, were selected as representatives of the endpoint members of two distinct types of genetic processes, i.e., mixed diagenetic/hydrogenetic and purely hydrogenetic. High-resolution analyses pursued the main aim of [...] Read more.
Two Fe–Mn crusts among 35 samples, from six seamounts in the Canary Island Seamount Province, were selected as representatives of the endpoint members of two distinct types of genetic processes, i.e., mixed diagenetic/hydrogenetic and purely hydrogenetic. High-resolution analyses pursued the main aim of distinguishing the critical elements and their association with mineral phases and genetic processes forming a long-lived Fe–Mn crust. The Fe–Mn crust collected on the Tropic Seamount is composed of dense laminations of Fe-vernadite (>90%) and goethite group minerals, reflecting the predominance of the hydrogenetic process during their formation. Based on high-resolution age calculation, this purely hydrogenetic crust yielded an age of 99 Ma. The Fe–Mn crust collected on the Paps Seamount shows a typical botryoidal surface yielding an age of 30 Ma. electron probe microanalyzer (EPMA) spot analyses show two main types of manganese oxides, indicating their origin: (i) hydrogenetic Fe-vernadite, the main Mn oxide, and (ii) laminations of interlayered buserite and asbolane. Additionally, the occurrence of calcite, authigenic carbonate fluor-apatite (CFA) and palygorskite suggests early diagenesis and pervasive phosphatization events. Sequential leaching analysis indicated that Co, Ni, Cu, Ba and Ce are linked to Mn minerals. Therefore, Mn-oxides are enriched in Ni and Cu by diagenetic processes or in Co and Ce by hydrogenetic processes. On the other hand, Fe-oxides concentrate V, Zn, As and Pb. Moreover, the evidence of HREE enrichment related to Fe-hydroxides is confirmed in the mixed hydrogenetic/diagenetic crust. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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31 pages, 3160 KiB  
Review
Lunar and Martian Silica
by Masahiro Kayama, Hiroshi Nagaoka and Takafumi Niihara
Minerals 2018, 8(7), 267; https://doi.org/10.3390/min8070267 - 25 Jun 2018
Cited by 22 | Viewed by 10660
Abstract
Silica polymorphs, such as quartz, tridymite, cristobalite, coesite, stishovite, seifertite, baddeleyite-type SiO2, high-pressure silica glass, moganite, and opal, have been found in lunar and/or martian rocks by macro-microanalyses of the samples and remote-sensing observations on the celestial bodies. Because each silica [...] Read more.
Silica polymorphs, such as quartz, tridymite, cristobalite, coesite, stishovite, seifertite, baddeleyite-type SiO2, high-pressure silica glass, moganite, and opal, have been found in lunar and/or martian rocks by macro-microanalyses of the samples and remote-sensing observations on the celestial bodies. Because each silica polymorph is stable or metastable at different pressure and temperature conditions, its appearance is variable depending on the occurrence of the lunar and martian rocks. In other words, types of silica polymorphs provide valuable information on the igneous process (e.g., crystallization temperature and cooling rate), shock metamorphism (e.g., shock pressure and temperature), and hydrothermal fluid activity (e.g., pH and water content), implying their importance in planetary science. Therefore, this article focused on reviewing and summarizing the representative and important investigations of lunar and martian silica from the viewpoints of its discovery from lunar and martian materials, the formation processes, the implications for planetary science, and the future prospects in the field of “micro-mineralogy”. Full article
(This article belongs to the Special Issue Mineralogy of Quartz and Silica Minerals)
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10 pages, 2797 KiB  
Article
Fiemmeite Cu2(C2O4)(OH)2∙2H2O, a New Mineral from Val di Fiemme, Trentino, Italy
by Francesco Demartin, Italo Campostrini, Paolo Ferretti and Ivano Rocchetti
Minerals 2018, 8(6), 248; https://doi.org/10.3390/min8060248 - 12 Jun 2018
Cited by 6 | Viewed by 7598
Abstract
The new mineral species fiemmeite, Cu2(C2O4)(OH)2∙2H2O, was found NE of the Passo di San Lugano, Val di Fiemme, Carano, Trento, Italy (latitude 46.312° N, longitude 11.406° E). It occurs in coalified woods [...] Read more.
The new mineral species fiemmeite, Cu2(C2O4)(OH)2∙2H2O, was found NE of the Passo di San Lugano, Val di Fiemme, Carano, Trento, Italy (latitude 46.312° N, longitude 11.406° E). It occurs in coalified woods at the base of the Val Gardena Sandstone (upper Permian) which were permeated by mineralizing solutions containing Cu, U, As, Pb and Zn. The oxalate anions have originated from diagenesis of the plant remains included in sandstones. The mineral forms aggregate up to 1 mm across of sky blue platelets with single crystals reaching maximum dimensions of about 50 μm. Associated minerals are: baryte, olivenite, middlebackite, moolooite, brochantite, cuprite, devilline, malachite, azurite, zeunerite/metazeunerite, tennantite, chalcocite, galena. Fiemmeite is monoclinic, space group: P21/c with a = 3.4245(6), b = 10.141(2), c = 19.397(3) Å, β = 90.71(1)°, V = 673.6(2) Å3, Z = 4. The calculated density is 2.802 g/cm3 while the observed density is 2.78(1) g/cm3. The six strongest reflections in the X-ray powder diffraction pattern are: [dobs in Å (I)(hkl)] 5.079(100)(020), 3.072(58)(112), 9.71(55)(002), 4.501(50)(022), 7.02(28)(012), 2.686(25)(114). The crystal structure was refined from single-crystal data to a final R1 = 0.0386 for 1942 observed reflections [I > 2σ(I)] with all the hydrogen atoms located from a Difference–Fourier map. The asymmetric unit contains two independent Cu2+ cations that display a distorted square-bipyramidal (4+2) coordination, one oxalate anion, two hydroxyl anions and two water molecules. The coordination polyhedra of the two copper atoms share common edges to form polymeric rows running along [100] with composition [Cu2(C2O4)(OH)2∙2H2O]n. These rows are held together by a well-established pattern of hydrogen bonds between the oxalate oxygens not involved in the coordination to copper, the hydrogen atoms of the water molecules and the hydroxyl anions. Full article
(This article belongs to the Special Issue New Mineral Species and Their Crystal Structures)
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21 pages, 3321 KiB  
Article
Si-Disordering in MgAl2O4-Spinel under High P-T Conditions, with Implications for Si-Mg Disorder in Mg2SiO4-Ringwoodite
by Liping Liu, Xi Liu, Xinjian Bao, Qiang He, Wei Yan, Yunlu Ma, Mingyue He, Renbiao Tao and Ruqiang Zou
Minerals 2018, 8(5), 210; https://doi.org/10.3390/min8050210 - 12 May 2018
Cited by 17 | Viewed by 7948
Abstract
A series of Si-bearing MgAl2O4-spinels were synthesized at 1500–1650 °C and 3–6 GPa. These spinels had SiO2 contents of up to ~1.03 wt % and showed a substitution mechanism of Si4+ + Mg2+ = 2Al3+ [...] Read more.
A series of Si-bearing MgAl2O4-spinels were synthesized at 1500–1650 °C and 3–6 GPa. These spinels had SiO2 contents of up to ~1.03 wt % and showed a substitution mechanism of Si4+ + Mg2+ = 2Al3+. Unpolarized Raman spectra were collected from polished single grains, and displayed a set of well-defined Raman peaks at ~610, 823, 856 and 968 cm−1 that had not been observed before. Aided by the Raman features of natural Si-free MgAl2O4-spinel, synthetic Si-free MgAl2O4-spinel, natural low quartz, synthetic coesite, synthetic stishovite and synthetic forsterite, we infer that these Raman peaks should belong to the SiO4 groups. The relations between the Raman intensities and SiO2 contents of the Si-bearing MgAl2O4-spinels suggest that under some P-T conditions, some Si must adopt the M-site. Unlike the SiO4 groups with very intense Raman signals, the SiO6 groups are largely Raman-inactive. We further found that the Si cations primarily appear on the T-site at P-T conditions ≤~3–4 GPa and 1500 °C, but attain a random distribution between the T-site and M-site at P-T conditions ≥~5–6 GPa and 1630–1650 °C. This Si-disordering process observed for the Si-bearing MgAl2O4-spinels suggests that similar Si-disordering might happen to the (Mg,Fe)2SiO4-spinels (ringwoodite), the major phase in the lower part of the mantle transition zone of the Earth and the benchmark mineral for the very strong shock stage experienced by extraterrestrial materials. The likely consequences have been explored. Full article
(This article belongs to the Special Issue Spinel Group Minerals)
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26 pages, 6657 KiB  
Article
The Carbonation of Wollastonite: A Model Reaction to Test Natural and Biomimetic Catalysts for Enhanced CO2 Sequestration
by Fulvio Di Lorenzo, Cristina Ruiz-Agudo, Aurelia Ibañez-Velasco, Rodrigo Gil-San Millán, Jorge A. R. Navarro, Encarnacion Ruiz-Agudo and Carlos Rodriguez-Navarro
Minerals 2018, 8(5), 209; https://doi.org/10.3390/min8050209 - 11 May 2018
Cited by 54 | Viewed by 10512
Abstract
One of the most promising strategies for the safe and permanent disposal of anthropogenic CO2 is its conversion into carbonate minerals via the carbonation of calcium and magnesium silicates. However, the mechanism of such a reaction is not well constrained, and its [...] Read more.
One of the most promising strategies for the safe and permanent disposal of anthropogenic CO2 is its conversion into carbonate minerals via the carbonation of calcium and magnesium silicates. However, the mechanism of such a reaction is not well constrained, and its slow kinetics is a handicap for the implementation of silicate mineral carbonation as an effective method for CO2 capture and storage (CCS). Here, we studied the different steps of wollastonite (CaSiO3) carbonation (silicate dissolution → carbonate precipitation) as a model CCS system for the screening of natural and biomimetic catalysts for this reaction. Tested catalysts included carbonic anhydrase (CA), a natural enzyme that catalyzes the reversible hydration of CO2(aq), and biomimetic metal-organic frameworks (MOFs). Our results show that dissolution is the rate-limiting step for wollastonite carbonation. The overall reaction progresses anisotropically along different [hkl] directions via a pseudomorphic interface-coupled dissolution–precipitation mechanism, leading to partial passivation via secondary surface precipitation of amorphous silica and calcite, which in both cases is anisotropic (i.e., (hkl)-specific). CA accelerates the final carbonate precipitation step but hinders the overall carbonation of wollastonite. Remarkably, one of the tested Zr-based MOFs accelerates the dissolution of the silicate. The use of MOFs for enhanced silicate dissolution alone or in combination with other natural or biomimetic catalysts for accelerated carbonation could represent a potentially effective strategy for enhanced mineral CCS. Full article
(This article belongs to the Special Issue Mineral Surface Reactions at the Nanoscale)
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16 pages, 1425 KiB  
Article
Classical Polarizable Force Field to Study Hydrated Hectorite: Optimization on DFT Calculations and Validation against XRD Data
by Ragnhild Hånde, Vivien Ramothe, Stéphane Tesson, Baptiste Dazas, Eric Ferrage, Bruno Lanson, Mathieu Salanne, Benjamin Rotenberg and Virginie Marry
Minerals 2018, 8(5), 205; https://doi.org/10.3390/min8050205 - 10 May 2018
Cited by 12 | Viewed by 5547
Abstract
Following our previous works on dioctahedral clays, we extend the classical Polarizable Ion Model (PIM) to trioctahedral clays, by considering dry Na-, Cs-, Ca- and Sr-hectorites as well as hydrated Na-hectorite. The parameters of the force field are determined by optimizing the atomic [...] Read more.
Following our previous works on dioctahedral clays, we extend the classical Polarizable Ion Model (PIM) to trioctahedral clays, by considering dry Na-, Cs-, Ca- and Sr-hectorites as well as hydrated Na-hectorite. The parameters of the force field are determined by optimizing the atomic forces and dipoles on density functional theory calculations. The simulation results are validated by comparison with experimental X-ray diffraction (XRD) data. The XRD patterns calculated from classical molecular dynamics simulations performed with the PIM force field are in very good agreement with experimental results. In the bihydrated state, the less structured electronic density profile obtained with PIM compared to the one from the state-of-the-art non-polarizable force field clayFF explains the slightly better agreement between the PIM results and experiments. Full article
(This article belongs to the Special Issue Molecular Simulation of Mineral-Solution Interfaces)
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31 pages, 7578 KiB  
Article
Linkages between the Genesis and Resource Potential of Ferromanganese Deposits in the Atlantic, Pacific, and Arctic Oceans
by Amaya Menendez, Rachael James, Natalia Shulga, Doug Connelly and Steve Roberts
Minerals 2018, 8(5), 197; https://doi.org/10.3390/min8050197 - 5 May 2018
Cited by 9 | Viewed by 5688
Abstract
In addition to iron and manganese, deep sea ferromanganese deposits, including nodules and crusts, contain significant amounts of economically interesting metals, such as cobalt (Co), nickel (Ni), copper (Cu), and rare Earth elements and yttrium (REY). Some of these metals are essential in [...] Read more.
In addition to iron and manganese, deep sea ferromanganese deposits, including nodules and crusts, contain significant amounts of economically interesting metals, such as cobalt (Co), nickel (Ni), copper (Cu), and rare Earth elements and yttrium (REY). Some of these metals are essential in the development of emerging and new-generation green technologies. However, the resource potential of these deposits is variable, and likely related to environmental conditions that prevail as they form. To better assess the environmental controls on the resource potential of ferromanganese deposits, we have undertaken a detailed study of the chemical composition of ferromanganese nodules and one crust sample from different oceanic regions. Textural and chemical characteristics of nodules from the North Atlantic and a crust from the South Pacific suggest that they acquire metals from a hydrogenous source. These deposits are potentially an economically important source of Co and the REY. On the other hand, nodules from the Pacific Ocean represent a marginal resource of these metals, due to their relatively fast growth rate caused by diagenetic precipitation. By contrast, they have relatively high concentrations of Ni and Cu. A nodule from the Arctic Ocean is characterised by the presence of significant quantities of detrital silicate material, which significantly reduces their metal resource. Full article
(This article belongs to the Special Issue Deep-Sea Minerals and Gas Hydrates)
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13 pages, 463 KiB  
Commentary
How Can Additives Control the Early Stages of Mineralisation?
by Denis Gebauer
Minerals 2018, 8(5), 179; https://doi.org/10.3390/min8050179 - 26 Apr 2018
Cited by 66 | Viewed by 8059
Abstract
The interactions between additives and mineral precursors and intermediates are at the heart of additive-controlled crystallisation, which is of high importance for various fields. In this commentary, we reflect on potential modes of additive control according to classical nucleation theory on one hand, [...] Read more.
The interactions between additives and mineral precursors and intermediates are at the heart of additive-controlled crystallisation, which is of high importance for various fields. In this commentary, we reflect on potential modes of additive control according to classical nucleation theory on one hand, and from the viewpoint of the so-called pre-nucleation cluster pathway on the other. This includes a brief review of the corresponding literature. While the roles of additives are discussed generally, i.e., without specific chemical or structural details, corresponding properties are outlined where possible. Altogether, our discussion illustrates that “non-classical” nucleation pathways promise an improved understanding of additive-controlled scenarios, which could be utilised in targeted applications in various fields, ranging from scale inhibition to materials chemistry. Full article
(This article belongs to the Special Issue Mineral Surface Reactions at the Nanoscale)
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31 pages, 7281 KiB  
Article
The Hydrothermal Breccia of Berglia-Glassberget, Trøndelag, Norway: Snapshot of a Triassic Earthquake
by Axel Müller, Morgan Ganerød, Michael Wiedenbeck, Skule Olaus Svendsen Spjelkavik and Rune Selbekk
Minerals 2018, 8(5), 175; https://doi.org/10.3390/min8050175 - 23 Apr 2018
Cited by 5 | Viewed by 9544
Abstract
The quartz-K-feldspar-cemented breccia of Berglia-Glassberget in the Lierne municipality in central Norway forms an ellipsoid structure 250 m × 500 m in size. The hydrothermal breccia is barren in terms of economic commodities but famous among mineral collectors for being a large and [...] Read more.
The quartz-K-feldspar-cemented breccia of Berglia-Glassberget in the Lierne municipality in central Norway forms an ellipsoid structure 250 m × 500 m in size. The hydrothermal breccia is barren in terms of economic commodities but famous among mineral collectors for being a large and rich site of crystal quartz of various colours and habits. Despite being a famous collector site, the mineralization is rather unique in respect to its geological setting. It occurs within Late Palaeoproterozoic metarhyolites of the Lower Allochthon of the Norwegian Caledonides regionally isolated from any other contemporaneous hydrothermal or magmatic event. In order to understand better the formation of the Berglia-Glassberget breccia, the chemistry, fluid inclusion petrography and age of the breccia cement were determined. Structural features indicate that the Berglia-Glassberget is a fault-related, fluid-assisted, hydraulic breccia which formed by single pulse stress released by a seismic event. 40Ar-39Ar dating of K-feldspar cement revealed a middle Triassic age (240.3 ± 0.4 Ma) for this event. The influx into the fault zone of an aqueous CO2-bearing fluid triggered the sudden fault movement. The high percentage of open space in the breccia fractures with cavities up 3 m × 3 m × 4 m in size, fluid inclusion microthermometry, and trace element chemistry of quartz suggests that the breccia was formed at depths between 4 and 0.5 km (1.1 to 0.1 kbar). The origin of the breccia-cementing, CO2-bearing Na-HCO3-SO4 fluid may have been predominantly of metamorphic origin due to decarbonation reactions (T > 200 °C) of limestones of the underlying Olden Nappe. The decarbonation reactions were initiated by deeply derived, hot fluids channelled to sub-surface levels by a major fault zone, implying that the breccia is situated on a deep-seated structure. Regionally, the Berglia-Glassberget occurs at a supposed triple junction of long-lived fault zones belonging to the Møre-Trøndelag, Lærdal-Gjende and the Kollstraumen fault complexes. These fault systems and the associated Berglia-Glassberget earthquake are the expression of rifting and faulting in northern Europe during the middle/late Triassic. Full article
(This article belongs to the Special Issue Mineralogy of Quartz and Silica Minerals)
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14 pages, 4227 KiB  
Article
New Mineral with Modular Structure Derived from Hatrurite from the Pyrometamorphic Rocks of the Hatrurim Complex: Ariegilatite, BaCa12(SiO4)4(PO4)2F2O, from Negev Desert, Israel
by Evgeny V. Galuskin, Biljana Krüger, Irina O. Galuskina, Hannes Krüger, Yevgeny Vapnik, Justyna A. Wojdyla and Mikhail Murashko
Minerals 2018, 8(3), 109; https://doi.org/10.3390/min8030109 - 8 Mar 2018
Cited by 17 | Viewed by 6481
Abstract
Ariegilatite, BaCa12(SiO4)4(PO4)2F2O (R 3 ¯ m, a = 7.1551(6) Å, c = 41.303(3) Å, V = 1831.2(3) Å3, Z = 3), is a new member of the [...] Read more.
Ariegilatite, BaCa12(SiO4)4(PO4)2F2O (R 3 ¯ m, a = 7.1551(6) Å, c = 41.303(3) Å, V = 1831.2(3) Å3, Z = 3), is a new member of the nabimusaite group exhibiting a modular intercalated antiperovskite structure derived from hatrurite. It was found in a few outcrops of pyrometamorphic rocks of the Hatrurim Complex located in the territories of Israel, Palestine and Jordan. The holotype specimen is an altered spurrite marble from the Negev Desert near Arad city, Israel. Ariegilatite is associated with spurrite, calcite, brownmillerite, shulamitite, CO3-bearing fluorapatite, fluormayenite-fluorkyuygenite and a potentially new mineral, Ba2Ca18(SiO4)6(PO4)3(CO3)F3O. Ariegilatite is overgrown and partially replaced by stracherite, BaCa6(SiO4)2[(PO4)(CO3)]F. The mineral forms flat disc-shaped crystals up to 0.5 mm in size. It is colorless, transparent, with white steaks and vitreous luster. Optically, ariegilatite is uniaxial, negative: ω = 1.650(2), ε = 1.647(2) (λ = 589 nm). The mean composition of the holotype ariegilatite, (Ba0.98K0.01Na0.01)Σ1(Ca11.77Na0.08Fe2+0.06Mn2+0.05Mg0.04)Σ12(Si3.95Al0.03Ti0.02)Σ4(P1.70C0.16Si0.10S6+0.03V0.01)Σ2F2.04O0.96, is close to the end-member formula. The structure of ariegilatite is described as a stacking of the two modules {F2OCa12(SiO4)4}4+ and {Ba(PO4)2}4− along (001). Ariegilatite, as well as associated stracherite, are high-temperature alteration products of minerals of an early clinker-like association. These alterations took place under the influence of pyrometamorphism by-products, such as gases and fluids generated by closely-spaced combustion foci. Full article
(This article belongs to the Special Issue New Mineral Species and Their Crystal Structures)
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28 pages, 4946 KiB  
Article
Mineralogical Distribution of Germanium, Gallium and Indium at the Mt Carlton High-Sulfidation Epithermal Deposit, NE Australia, and Comparison with Similar Deposits Worldwide
by Fredrik Sahlström, Antonio Arribas, Paul Dirks, Isaac Corral and Zhaoshan Chang
Minerals 2017, 7(11), 213; https://doi.org/10.3390/min7110213 - 5 Nov 2017
Cited by 53 | Viewed by 12018
Abstract
Germanium, gallium and indium are in high demand due to their growing usage in high-tech and green-tech applications. However, the mineralogy and the mechanisms of concentration of these critical elements in different types of hydrothermal ore deposits remain poorly constrained. We investigated the [...] Read more.
Germanium, gallium and indium are in high demand due to their growing usage in high-tech and green-tech applications. However, the mineralogy and the mechanisms of concentration of these critical elements in different types of hydrothermal ore deposits remain poorly constrained. We investigated the mineralogical distribution of Ge, Ga and In at the Mt Carlton high-sulfidation epithermal deposit in NE Australia, using electron probe microanalysis and laser ablation inductively-coupled plasma mass spectrometry. Parageneses from which selected minerals were analyzed include: Stage 1 acid sulfate alteration (alunite), Stage 2A high-sulfidation enargite mineralization (enargite, argyrodite, sphalerite, pyrite, barite), Stage 2B intermediate-sulfidation sphalerite mineralization (sphalerite, pyrite, galena) and Stage 3 hydrothermal void fill (dickite). Moderate to locally high concentrations of Ga were measured in Stage 1 alunite (up to 339 ppm) and in Stage 3 dickite (up to 150 ppm). The Stage 2A ores show enrichment in Ge, which is primarily associated with argyrodite (up to 6.95 wt % Ge) and Ge-bearing enargite (up to 2189 ppm Ge). Co-existing sphalerite has comparatively low Ge content (up to 143 ppm), while Ga (up to 1181 ppm) and In (up to 571 ppm) are higher. Sphalerite in Stage 2B contains up to 611 ppm Ge, 2829 ppm Ga and 2169 ppm In, and locally exhibits fine colloform bands of an uncharacterized Zn-In mineral with compositions close to CuZn2(In,Ga)S4. Barite, pyrite and galena which occur in association with Stage 2 mineralization were found to play negligible roles as carriers of Ge, Ga and In at Mt Carlton. Analyzed reference samples of enargite from seven similar deposits worldwide have average Ge concentrations ranging from 12 to 717 ppm (maximum 2679 ppm). The deposits from which samples showed high enrichment in critical elements in this study are all hosted in stratigraphic sequences that locally contain carbonaceous sedimentary rocks. In addition to magmatic-hydrothermal processes, such rocks could potentially be important for the concentration of critical elements in high-sulfidation epithermal deposits. Full article
(This article belongs to the Special Issue Mineral Deposits of Critical Elements)
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19 pages, 34339 KiB  
Article
Trace Element Compositions and Defect Structures of High-Purity Quartz from the Southern Ural Region, Russia
by Jens Götze, Yuanming Pan, Axel Müller, Elena L. Kotova and Daniele Cerin
Minerals 2017, 7(10), 189; https://doi.org/10.3390/min7100189 - 11 Oct 2017
Cited by 33 | Viewed by 8017
Abstract
Quartz samples of different origin from 10 localities in the Southern Ural region, Russia have been investigated to characterize their trace element compositions and defect structures. The analytical combination of cathodoluminescence (CL) microscopy and spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and trace-element analysis [...] Read more.
Quartz samples of different origin from 10 localities in the Southern Ural region, Russia have been investigated to characterize their trace element compositions and defect structures. The analytical combination of cathodoluminescence (CL) microscopy and spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and trace-element analysis by inductively coupled plasma mass spectrometry (ICP-MS) revealed that almost all investigated quartz samples showed very low concentrations of trace elements (cumulative concentrations of <50 ppm with <30 ppm Al and <10 ppm Ti) and low abundances of paramagnetic defects, defining them economically as “high-purity” quartz (HPQ) suitable for high-tech applications. EPR and CL data confirmed the low abundances of substitutional Ti and Fe, and showed Al to be the only significant trace element structurally bound in the investigated quartz samples. CL microscopy revealed a heterogeneous distribution of luminescence centres (i.e., luminescence active trace elements such as Al) as well as features of deformation and recrystallization. It is suggested that healing of defects due to deformation-related recrystallization and reorganization processes of the quartz lattice during retrograde metamorphism resulted in low concentrations of CL activator and other trace elements or vacancies, and thus are the main driving processes for the formation of HPQ deposits in the investigated area. Full article
(This article belongs to the Special Issue Mineralogy of Quartz and Silica Minerals)
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