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A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Crystallography and Physical Chemistry of Minerals & Nanominerals".

Deadline for manuscript submissions: closed (30 April 2019) | Viewed by 54962

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Dr. Davide Lenaz

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Department of Mathematics, Informatics and Geosciences, Università degli Studi di Trieste, 34128 Trieste, Italy
Interests: mineralogy; geochemistry; igneous petrology; mantle oxidation; sedimentary petrology
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Special Issue Information

Dear Colleagues,

Members of the spinel group are frequent accessory minerals of both igneous and metamorphic rocks and also occur as detrital grains in many sediments. Some of them, as magnetite and chromite, may be locally abundant and occur as monomineralic masses, pods, or layers.

This Special Issue will focus on recent advances in the study of natural spinels from different geological setting, from deep in the Earth to meteorites, including detrital ones. These studies will include new advances via several different spectroscopic methods (IR, Raman, Mössbauer, XANES, and so on), as well as provenance studies for detrital spinels or geochemical studies, including trace elements.

As spinels can be quite important in industrial application too, studies on synthetic spinels will be considered as well.

The aim of this Special Issue is to bring together researchers from different fields to acquire new knowledge on their geological history and successive transformations, as well as new achievements in possible industrial applications.

Dr. Davide Lenaz
Guest Editor

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Minerals is an international peer-reviewed open access monthly journal published by MDPI.

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Keywords

Structure
Chemistry
Isotopes
Experimental works
Paragenesis
Spectroscopy
Oxygen fugacity
Industrial application

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Related Special Issue

Spinel Group Minerals, Volume II in Minerals (4 articles)

Published Papers (10 papers)

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Research

Jump to: Review

15 pages, 7164 KiB

Open AccessCommunication

First Detection of Methane within Chromitites of an Archean-Paleoproterozoic Greenstone Belt in Brazil

by Yuri de Melo Portella, Federica Zaccarini and Giuseppe Etiope

Minerals 2019, 9(5), 256; https://doi.org/10.3390/min9050256 - 29 Apr 2019

Cited by 6 | Viewed by 3183

Abstract

Abiotic methane is widely documented in seeps, springs and aquifers associated with mafic-ultramafic rocks in Phanerozoic ophiolites, peridotite massifs and intrusions worldwide. Chromitites in ophiolites, in particular, have been interpreted as the rocks potentially generating methane though CO₂ hydrogenation. Here, we document, for the first time, the presence of methane within chromitites in South America. We analyzed, through milling and gas extraction, the content of gas occluded in Cedrolina chromitite samples, belonging to the Pilar de Goiás greenstone belt in Brazil. The chromitites display significant gas concentrations up to 0.31 µg CH₄/g_rock and 2800 ppmv of hydrogen, while the host talc schist is devoid of gas. Stable C isotope composition of methane (δ¹³C from −30 to −39.2‰) and the absence of organic-matter rich metasediments in the region suggest an abiotic origin. Hydrogen and methane concentrations appear related to high-Cr chromite modal content and to the presence of Ni-sulfides/alloys, which are potential catalysts of CO₂ hydrogenation at temperatures above 200 °C. Accessory ruthenium-bearing minerals occurring in the chromitites could also act as catalysts, even at lower temperatures. Geothermometry of chlorite found in the chromitites constrains serpentinization at ~250 °C, during lower greenschist facies retrometamorphism. Hydrogen could be autochthonous, and thus formed under similar temperature, which we hypothesize represents the upper limit for abiotic methane generation in the area (250 °C). The Cedrolina chromitites are the first example of CH₄ occurrence in ultramafic rocks related to an Archean-Paleoproterozoic greenstone belt. This may imply that serpentinized Cr-rich chromitites could have been sources of methane for the early Earth’s atmosphere. Full article

(This article belongs to the Special Issue Spinel Group Minerals)

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18 pages, 3649 KiB

Open AccessEditor’s ChoiceArticle

Occurrence of Graphite-Like Carbon in Podiform Chromitites of Greece and Its Genetic Significance

by Maria Economou-Eliopoulos, George Tsoupas and Vasilis Skounakis

Minerals 2019, 9(3), 152; https://doi.org/10.3390/min9030152 - 3 Mar 2019

Cited by 8 | Viewed by 4424

Abstract

The role of post-magmatic processes in the composition of chromitites hosted in ophiolite complexes, the origin of super-reduced phases, and factors controlling the carbon recycling in a supra-subduction zone environment are still unclear. The present contribution compiles the first scanning electron microscope/energy-dispersive (SEM/EDS) data on graphite-like amorphous carbon, with geochemical and mineral chemistry data, from chromitites of the Skyros, Othrys, Pindos, and Veria ophiolites (Greece). The aim of this study was the delineation of potential relationships between the modified composition of chromite and the role of redox conditions, during the long-term evolution of chromitites in a supra-subduction zone environment. Chromitites are characterized by a strong brittle (cataclastic) texture and the presence of phases indicative of super-reducing phases, such as Fe–Ni–Cr-alloys, awaruite (Ni₃Fe), and heazlewoodite (Ni₃S₂). Carbon-bearing assemblages are better revealed on Au-coated unpolished sections. Graphite occurs in association with hydrous silicates (chlorite, serpentine) and Fe²⁺-chromite, as inclusions in chromite, filling cracks within chromite, or as nodule-like graphite aggregates. X-ray spectra of graphite–silicate aggregates showed the presence of C, Si, Mg, Al, O in variable proportions, and occasionally K and Ca. The extremely low fO₂ during serpentinization facilitated the occurrence of methane in microfractures of chromitites, the precipitation of super-reducing phases (metal alloys, awaruite, heazlewoodite), and graphite. In addition, although the origin of Fe–Cu–Ni-sulfides in ultramafic parts of ophiolite complexes is still unclear, in the case of the Othrys chromitites, potential reduction-induced sulfide and/or carbon saturation may drive formation of sulfide ores and graphite-bearing chromitites. The presented data on chromitites covering a wide range in platinum-group element (PGE) content, from less than 100 ppb in the Othrys to 25 ppm ΣPGE in the Veria ores, showed similarity in the abundance of graphite-like carbon. The lack of any relationship between graphite (and probably methane) and the PGE content may be related to the occurrence of the (Ru–Os–Ir) minerals in chromitites, which occur mostly as oxides/hydroxides, and to lesser amounts of laurite, with pure Ru instead activating the stable CO₂ molecule and reducing it to methane (experimental data from literature). Full article

(This article belongs to the Special Issue Spinel Group Minerals)

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8 pages, 1361 KiB

Open AccessArticle

Equation of State of a Natural Chromian Spinel at Ambient Temperature

by Zhongying Mi, Weiguang Shi, Lifei Zhang, Sean R. Shieh and Xi Liu

Minerals 2018, 8(12), 591; https://doi.org/10.3390/min8120591 - 13 Dec 2018

Cited by 6 | Viewed by 3113

Abstract

A natural chromian spinel with the composition (Mg_0.48(3)Fe_0.52(3))(Fe_0.06(1)Al_0.28(1)Cr_0.66(2))₂O₄ was investigated up to 15 GPa via synchrotron X-ray diffraction with a diamond-anvil cell at room temperature. No phase transition was clearly observed up to the maximum experimental pressure. The pressure–volume data fitted to the third-order Birch–Murnaghan equation of state yielded an isothermal bulk modulus (

K_{T 0}

) of 207(5) GPa and its first pressure derivative (

K_{T 0}^{'}

) of 3.2(7), or

K_{T 0}

= 202(2) GPa with

K_{T 0}^{'}

fixed as 4. With this new experimental result and the results on some natural chromian spinels in the literature, a simple algorithm describing the relation between the

K_{T 0}

and the compositions of the natural chromian spinels was proposed. To examine this algorithm further, more compression experiments should be performed on natural chromian spinels with different chemical compositions. Full article

(This article belongs to the Special Issue Spinel Group Minerals)

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24 pages, 6197 KiB

Open AccessArticle

Is Cr-Spinel Geochemistry Enough for Solving the Provenance Dilemma? Case Study from the Palaeogene Sandstones of the Western Carpathians (Eastern Slovakia)

by Katarína Bónová, Tomáš Mikuš and Ján Bóna

Minerals 2018, 8(12), 543; https://doi.org/10.3390/min8120543 - 23 Nov 2018

Cited by 19 | Viewed by 4142

Abstract

The provenance of the Proč and Strihovce sandstones is crucial for understanding the relationship between the Pieniny Klippen (PKB) and Flysch (FB) belts in the easternmost part of the Western Carpathian realm. Detrital Cr-spinels in these tectonic units were assertively interpreted as sourced from the southern sources representing the Meliata mélange. In this study, we use the geochemistry of detrital chromian spinels to identify the mafic and ultramafic source of the sediments and to compare them each other. Simultaneously, we compare their chemical compositions with those from the different Western Carpathian geological units, which could feed the Proč and Krynica basins during the Paleogene, where the Proč and Strihovce formations (fms), respectively, were deposited. Chromian spinels from the Proč and Strihovce fms exhibit similar geochemical characteristics (Cr# = 0.44–0.88 and 0.29–0.89, Mg# = 0.17–0.68 and 0.2–0.72, TiO₂ = 0.0–3.67 and 0.01–2.08 wt.%, respectively). The spinels show both supra-subduction zone (SSZ) peridotite signatures and volcanic origin. Whereas volcanic spinels from the Proč Formation (Fm.) were formed under an ocean island basalt (OIB) and back-arc basin basalt (BABB) geodynamic setting, those from the Strihovce Fm. suggest a predominantly mid-ocean ridge basalt (MORB) origin. To avoid mistakes in the provenance interpretations, the data from garnet geochemistry of both formations is supplied. The analysed Cr-spinels do not absolutely overlap with spinels reported from the Meliata Unit, and their composition indicates at least two independent sources. Full article

(This article belongs to the Special Issue Spinel Group Minerals)

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22 pages, 9843 KiB

Open AccessArticle

Copper-Containing Magnesioferrite in Vesicular Trachyandesite in a Lava Tube from the 2012–2013 Eruption of the Tolbachik Volcano, Kamchatka, Russia

by Victor V. Sharygin, Vadim S. Kamenetsky, Liudmila M. Zhitova, Alexander B. Belousov and Adam Abersteiner

Minerals 2018, 8(11), 514; https://doi.org/10.3390/min8110514 - 8 Nov 2018

Cited by 6 | Viewed by 5542

Abstract

Cu-rich magnesioferrite was found in vesicular basaltic trachyandesite in one of lava tubes (Duplex) that formed during the 2012–2013 eruption of the Tolbachik volcano, Kamchatka. This mineral is commonly associated with hematite, tenorite, halite, sylvite, and Ca-rich silicates (mainly, esseneite and Na-rich melilite) in high-temperature (800–1000 °C) reactionary zones (up to 100 µm) covering vesicular rocks and lava stalactites in the Duplex tube. The mineral relationships of this assemblage indicate the following crystallization sequence: Ca-rich silicates + hematite → Cu-rich magnesioferrite → tenorite → chlorides. This formed due to the reaction of hot gases containing Cu, alkalis, and Cl with solidified lava rock. The composition of magnesioferrite varies strongly in CuO (5.8–17.3 wt %; cuprospinel end-member—15–47 mol %), whereas the contents of other oxides are minor, indicating the main isomorphic substitution is Mg²⁺ ↔ Cu²⁺. Compositions with maximal CuO content nominally belong to Mg-rich cuprospinel: (Cu_0.48Mg_0.41Mn_0.09Zn_0.02Ca_0.02) (Fe³⁺_1.94Al_0.03Ti_0.02)O₄. Increasing CuO content of the Duplex Cu-rich magnesioferrite is reflected in Raman spectra by moderate right shifting bands at ≈700–710 and 200–210 cm⁻¹ and the appearance of an additional band at 596 cm⁻¹. This supports the main isomorphic scheme and may indicate a degree of inversion in the spinel structure. Full article

(This article belongs to the Special Issue Spinel Group Minerals)

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39 pages, 50723 KiB

Open AccessArticle

An Integrated Model for Ilmenite, Al-Spinel, and Corundum Exsolutions in Titanomagnetite from Oxide-Rich Layers of the Lac Doré Complex (Québec, Canada)

by Jean-Philippe Arguin, Philippe Pagé, Sarah-Jane Barnes, Réjean Girard and Charley Duran

Minerals 2018, 8(11), 476; https://doi.org/10.3390/min8110476 - 24 Oct 2018

Cited by 27 | Viewed by 7474

Abstract

The titanomagnetite of the Lac Doré Complex, an Archean layered intrusion that is located in the Abitibi greenstone belt in Québec (Canada), contains a wide variety of exsolution textures, which are the remnants of a complex cooling history. In the present study, we reconstitute the decomposition stages of the original solid solution in order to explain the formation of ilmenite, Al-spinel (hercynite and gahnite), and corundum exsolutions in magnetite. This was conducted through a detailed mineralogical and textural examination and in situ determination of mineral chemistry. Our investigation reveals two discrete types of ilmenite exsolutions, which are ascribed, respectively, to the oxidation of ulvöspinel at temperatures above and below the magnetite-ulvöspinel solvus. Exsolutions of Al-spinel result from either a decrease in the solubility of the (FeZn)Al₂O₄ components upon cooling, or local excesses of Al and Zn due to the removal of ulvöspinel during the early oxidation. The origin of corundum is ascribed to the oxidation of pre-existing hercynite exsolutions. The trace element composition of the titanomagnetite indicates stratigraphic reversals in Cr, Mg, Co, Ti, and Si and important changes in redox conditions. We interpret this as a direct consequence of a major event of magma chamber replenishment, which strongly influenced the distribution of exsolutions. Full article

(This article belongs to the Special Issue Spinel Group Minerals)

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21 pages, 3321 KiB

Open AccessEditor’s ChoiceArticle

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 16 | Viewed by 7509

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⁺. 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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15 pages, 41742 KiB

Open AccessArticle

Origin of Reverse Zoned Cr-Spinels from the Paleoproterozoic Yanmenguan Mafic–Ultramafic Complex in the North China Craton

by Yang Bai, Ben-Xun Su, Yan Xiao, Davide Lenaz, Patrick Asamoah Sakyi, Zi Liang, Chen Chen and Sai-Hong Yang

Minerals 2018, 8(2), 62; https://doi.org/10.3390/min8020062 - 12 Feb 2018

Cited by 17 | Viewed by 6923

Abstract

We conducted petrological and mineral chemistry investigations of Cr-spinel in ultramafic rocks of the Yanmenguan mafic–ultramafic complex in the North China Craton. The Cr-spinel grains occur as inclusions in enstatite, tschermakite, phlogopite, and olivine, or as interstitial grains among the aforementioned silicate minerals, and show concentric or asymmetrical textures. Back-scattered electron and elemental images and compositional profiles of the spinel grains indicate the presence of Cr- and Fe-rich cores and Al- and Mg-rich rims. The host silicate minerals display a decrease in Al and Mg contents accompanied by an increase in Cr and Fe away from the spinel. These textures and compositional variations suggest that subsolidus elemental exchange more likely gave rise to the compositional zonation, resulting in the transfer of Al and Mg from the silicate minerals to the spinel. The Mn, Ni, and Ti contents in spinel and the major elements of olivine-hosted spinel are relatively stable during subsolidus elemental diffusion and thus are more reliable tracers of primary high-temperature processes. The temperature estimates reveal that the subsolidus diffusion might have occurred at 600–720 °C, which could be linked to the regional metamorphic event. Full article

(This article belongs to the Special Issue Spinel Group Minerals)

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15 pages, 6096 KiB

Open AccessArticle

Following the Amphibolite to Greenschist Metamorphic Path through the Structural Parameters of Spinels from Amsaga (Mauritania)

by Davide Lenaz, Henrik Skogby, Nicola Rigonat and Julien Berger

Minerals 2018, 8(1), 27; https://doi.org/10.3390/min8010027 - 18 Jan 2018

Cited by 5 | Viewed by 5032

Abstract

We investigated the crystal and structural behavior of several Cr-bearing spinels from the Archean chromitites of Amsaga (Mauritania). The chemical and structural data testified a retrograde metamorphism from amphibolite to greenschist facies, witnessed by relative changes in the amount of all the major oxides (Cr, Al, Mg, Fe²⁺, Fe³⁺), the relative proportion of Fe³⁺/Fe_tot as well as the structural parameters, including the cell edge and the oxygen coordinate. The general agreement between electron microprobe and Mössbauer data indicates that the analyzed spinels are stoichiometric. The structural data revealed that the oxygen positional parameter of amphibole-bearing samples is the highest observed among Cr-bearing spinels with similar Cr# and Mg#. Consequently, it is suggested that a structural study of detrital Cr-spinels could be important in discriminating an amphibole-chromitite source from an ophiolite source. Full article

(This article belongs to the Special Issue Spinel Group Minerals)

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Review

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16 pages, 6813 KiB

Open AccessReview

Spinels in Meteorites: Observation Using Mössbauer Spectroscopy

by Alevtina A. Maksimova, Andrey V. Chukin, Israel Felner and Michael I. Oshtrakh

Minerals 2019, 9(1), 42; https://doi.org/10.3390/min9010042 - 13 Jan 2019

Cited by 8 | Viewed by 5626

Abstract

In this mini-review, we consider the results of various meteorite studies using Mössbauer spectroscopy with a high velocity resolution in order to reveal the minor spectral components related to spinels such as chromite, hercynite, magnesiochromite, magnesioferrite and daubréelite in bulk meteorite matter or in some extracted phases. Spinels observation in the Mössbauer spectra is supported by characterization of the studied samples by means of optical and scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and magnetization measurements. Mössbauer parameters obtained for extraterrestrial spinels are compared with those obtained for terrestrial analogs published in the literature. Full article

(This article belongs to the Special Issue Spinel Group Minerals)

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