Crystals

2025

Jump to: 2024

19 pages, 3246 KiB

Open AccessArticle

Effect of Fungal Metabolism on Zn Minerals Formation: The Case of Aspergillus niger and Penicillium chrysogenum

by Katerina V. Sazanova, Marina S. Zelenskaya, Anatoliy V. Korneev, Elena V. Bakhvalova, Dmitry Yu. Vlasov and Olga V. Frank-Kamenetskaya

Crystals 2025, 15(2), 118; https://doi.org/10.3390/cryst15020118 - 23 Jan 2025

Viewed by 423

Abstract

Soil fungi are significantly resistant to heavy metals, which allows them to be used in biotechnologies for environmental bioremediation. In order to clarify the prospects for using the fungi in Zn-detoxifying technologies, we investigated in vitro the effect of fungal metabolism on Zn [...] Read more.

Soil fungi are significantly resistant to heavy metals, which allows them to be used in biotechnologies for environmental bioremediation. In order to clarify the prospects for using the fungi in Zn-detoxifying technologies, we investigated in vitro the effect of fungal metabolism on Zn minerals formation. The cultivation of fungi with different acid-producing activities (Aspergillus niger and Penicillium chrysogenum) was carried out in a liquid Czapek–Dox nutrient medium with Zn concentrations from 250 to 2000 µmol within 28 days. The quantitates of low-molecular-weight organic acids, phosphates, and hydrophosphates ions in the medium were determined through chromatography–mass spectrometry; analysis of biomineralization products was carried out through powder X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. It was found that Zn in concentrations 250–500 μmol acts as a physiologically essential element, activating the growth of fungal mycelium, while at high concentrations (1000–2000 μmol), Zn acts as a toxic heavy metal, inhibiting fungal growth. Zn also activates the formation of oxalic acid by both species of fungi. But A. niger strongly acidified the medium, while P. chrysogenum leaves the medium pH close to neutral or slightly alkaline. Oxalate and phosphate crystallization occur with the participation of both fungal species. The ratio of biogenic oxalates and phosphates is directly dependent on the acid-reducing capacity of fungi. The solid solutions of katsarosite–glushinskite of the isodimorphic series with the general formula (Zn,Mg)C₂O₄·2H₂O (Mg ions comes from Czapek–Dox medium) were detected at all Zn concentrations in a wide range of pH (from 2 to 9.0). The transition from monoclinic (α-modifications) to orthorhombic (β-modifications) occurs at the ratio Mg/Zn > 1. Fungal zinc phosphate hopeite Zn₃(PO₄)₂·4H₂O was formed at a near-neutral pH at high Zn concentrations (1000 and 2000 µmol/L). In the Zn example, it was shown that not only oxalate but also phosphate fungal biomineralization can be used for the environment detoxification of heavy metals. The application of phosphate biomineralization seems promising in the case of severe pollutions. To create a near-neutral medium favorable for the formation of phosphates, it is advisable to use soil fungi non-producing or weakly producing organic acids (for example, P. chrysogenum). Full article

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14 pages, 6446 KiB

Open AccessArticle

Comparative Study of Gemological and Spectroscopic Features and Coloration Mechanism of Three Types of Spodumene

by Zijia Zhou, Jing Liu, Kui He, Biao Yang and Yinghua Rao

Crystals 2025, 15(2), 109; https://doi.org/10.3390/cryst15020109 - 22 Jan 2025

Viewed by 331

Abstract

Spodumene is a characteristic mineral in lithium-rich granitic pegmatites, serving both as a valuable mineral resource and an important gem material. This study incorporates three different color varieties of spodumene—pink to violet, yellow-green, and colorless—into a unified research framework. X-ray powder diffraction (XRD), [...] Read more.

Spodumene is a characteristic mineral in lithium-rich granitic pegmatites, serving both as a valuable mineral resource and an important gem material. This study incorporates three different color varieties of spodumene—pink to violet, yellow-green, and colorless—into a unified research framework. X-ray powder diffraction (XRD), electron probe microanalyzer (EPMA), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, ultraviolet–visible spectroscopy (UV-Vis), and photoluminescence spectroscopy (PL) were employed to systematically analyze the chemical composition, crystal structure, and spectroscopic properties of spodumene. Furthermore, the coloration mechanism and fluorescence emission of the different color samples were investigated and analyzed. The results indicate that the presence and mixed valence states of the transition metals Fe and Mn primarily influence the color and photoluminescence of the three types of spodumene. Mn³⁺ is the primary color-causing element in pink to violet spodumene, while Fe³⁺ is the primary color-causing element in yellow-green spodumene. Photoluminescence in all three color varieties is dominated by Mn²⁺. These findings contribute to a deeper understanding of the color and luminescence mechanisms of spodumene, expanding its potential applications as both a gem material and a luminescent material. Full article

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17 pages, 15392 KiB

Open AccessArticle

Material and Technique Analysis of Qing Dynasty Official Style Architectural Polychrome Paintings in Hangzhou, Zhejiang, China

by Ling Shen, Dan Hua, Baisu Nan, Yao Yao, Hong Duan and Jiakun Wang

Crystals 2025, 15(1), 92; https://doi.org/10.3390/cryst15010092 - 19 Jan 2025

Viewed by 395

Abstract

Hangzhou was the political and economic center of the Southern Song Dynasty (1127–1279 AD) and also the southern end of the Beijing-Hangzhou Grand Canal during the Ming and Qing Dynasties (1368–1644 AD). This historical position allowed the city’s economy to develop rapidly and [...] Read more.

Hangzhou was the political and economic center of the Southern Song Dynasty (1127–1279 AD) and also the southern end of the Beijing-Hangzhou Grand Canal during the Ming and Qing Dynasties (1368–1644 AD). This historical position allowed the city’s economy to develop rapidly and influenced the form of its polychrome paintings with the imperial official style of the north China. However, due to the high temperature and rainy natural preservation conditions, southern polychrome paintings have always been a weak link in Chinese architectural polychrome painting craftsmanship. This study focuses on two well-preserved official-style architectural polychrome paintings in the grand halls from the late Qing period in Hangzhou. Through multi-techniques such as optical microscopy (OM), scanning electron microprobe with energy dispersive X-ray spectroscopy analysis (SEM-EDX), micro-Raman spectroscopy, micro-Fourier Transform Infrared spectroscopy (μ-FTIR), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), it was found that there is a significant difference from the reported common non-ground architectural paintings in the south, typically having four-layer structures with a white base and ground plaster layer in preparation for painting. The appearance of pigments such as artificial ultramarine (Na₆Al₄Si₆S₄O₂₀) and emerald green (Cu(C₂H₃O₂)₂·3Cu(AsO₂)₂) indicates that the paintings were made at least after the 1830s, and the use of malachite green dye and copper phthalocyanine blue (PB 15:X) suggests that unrecorded restorations were also performed after the 20th century. All samples are coated with a layer of alkyd resin, which may have been added during the repairs in the latter half of the 20th century, leading to the black discoloration of the present paintings, especially in areas where emerald green was used. This study provides an important case for the study of the official style of polychrome painting craftsmanship in the southern region of China and also offers important references for the future protection and restoration of traditional architectural polychrome painting. Full article

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16 pages, 5802 KiB

Open AccessArticle

Chromite and Its Thin Kosmochlor and Cr-Omphacite Cortex in Amphibolite from the Myanmar Jadeite Deposits

by Yu Zhang, Guanghai Shi and Jiabao Wen

Crystals 2025, 15(1), 79; https://doi.org/10.3390/cryst15010079 - 15 Jan 2025

Viewed by 433

Abstract

Chromite in the amphibolites of the Myanmar jadeite deposits has not been well studied. Mineralogical studies on chromite and related kosmochlor and Cr-omphacite in the amphibolite of the Myanmar jadeite deposits were conducted. Compared to the chromite in the adjacent serpentinized peridotite, the [...] Read more.

Chromite in the amphibolites of the Myanmar jadeite deposits has not been well studied. Mineralogical studies on chromite and related kosmochlor and Cr-omphacite in the amphibolite of the Myanmar jadeite deposits were conducted. Compared to the chromite in the adjacent serpentinized peridotite, the chromite had higher Cr₂O₃ (45.67–54.25 wt.%) and MnO (1.82–1.90 wt.%) but lower MgO (1.00–1.96 wt.%) and Al₂O₃ (1.05–15.09 wt.%), similar to the published chromite compositions in jadeitite. Serpentinite was derived from a highly depleted mantle peridotite. There were at least two stages of metasomatism during the transformation of serpentinite + chromite to magnesio-katophorite + chromite + thin kosmochlor (and/or Cr-omphacite cortex). The first stage was the Ca-rich metasomatism of serpentinite, resulting in sodic-calcic amphibole (magnesio-katophorite), which preceded the formation of jadeite. The second stage of Na-rich metasomatism was produced by the Na-Al-Si-rich fluids with the magnesio-katophorite + chromite (contemporaneous with the formation of jadeite). The composition of the fluid was altered by a reaction with magnesio-katophorite, increasing the Ca-Mg content and resulting in the formation of kosmochlor rich in Ca-Mg and/or peripheral Cr-omphacite. This kosmochlor–Cr-omphacite belongs to the Jd-Kos-Di ternary join, which differs from the kosmochlor–Cr-jadeite (which belongs to the Jd-Kos join in jadeitite). The formation of jadeitite with chromite + kosmochlor + Cr-jadeite occurs when large amounts of Na-Al-Si-rich fluids have wrapped the pieces of chromite-bearing amphibolite. This also explains the proverbial “moss spray green” given that amphibole (with chromite) brings out the green color in jadeitite. Full article

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27 pages, 24226 KiB

Open AccessArticle

Effect of Prewetting Cenospheres on Hydration Kinetics, Microstructure, and Mechanical Properties of Refractory Castables

by Ina Pundienė and Jolanta Pranckevičienė

Crystals 2025, 15(1), 68; https://doi.org/10.3390/cryst15010068 - 12 Jan 2025

Viewed by 394

Abstract

This study investigated the effect of non-prewetted and prewetted cenospheres (CSs) on the hydration course and physical and mechanical properties of refractory castable mixtures incorporated with nano silica (NS). The fixed amount of 0.1% of NS improves the compressive strength of the refractory [...] Read more.

This study investigated the effect of non-prewetted and prewetted cenospheres (CSs) on the hydration course and physical and mechanical properties of refractory castable mixtures incorporated with nano silica (NS). The fixed amount of 0.1% of NS improves the compressive strength of the refractory castable, containing various proportions of non-prewetted and prewetted CSs (up to 25% in composition). It was found that an increase in CSs slows down the hydration of cement and the early structure formation of refractory castable mixtures. Proportionally, due to the increase in the amount of non-prewetted and prewetted CSs in the composition, the density of the samples decreases from 1875 kg/m³ to 1310 kg/m³ after firing. The amount of CSs varied from 15 to 25% in the composition, increasing compressive strength by up to 5.3% and 8.6% in the case of non-prewetted CSs and by up to 39.2% and 20.5% in the case of prewetted CSs after the drying process. Prewetting CSs provides additional internal water that facilitates cement hydration during drying, promoting the formation of stratlingite (C₂ASH₈), a key hydration product that enhances mechanical properties after firing and promotes the early formation of anorthite. The firing at 800 °C and 1100 °C temperatures decreases compressive strength to a greater extent, as more CSs are in the composition. However, prewetting of CSs leads to significantly less deterioration (up to 32%, compared to compositions with non-prewetted CSs) in the compressive strength of refractory castables. The shrinkage of the refractory castable samples after firing at 1100 °C reached 0.16% in the case of non-prewetted CSs and 0.1% in the case of prewetted CSs. Prewetted CSs in refractory castables relaxes the stresses arising during firing more efficiently and practically compensates for shrinkage processes. Full article

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2024

Jump to: 2025

24 pages, 13065 KiB

Open AccessReview

Crystal Chemistry and Structural Complexity of the Uranyl Vanadate Minerals and Synthetic Compounds

by Ivan V. Kuporev, Sophia A. Kalashnikova and Vladislav V. Gurzhiy

Crystals 2025, 15(1), 43; https://doi.org/10.3390/cryst15010043 - 30 Dec 2024

Viewed by 588

Abstract

This paper reviews perhaps one of the most enigmatic groups of secondary uranium minerals. The number of uranyl vanadate mineral species does not reach even 20, and they do not display a large range of structural diversity, but those natural phases form rather [...] Read more.

This paper reviews perhaps one of the most enigmatic groups of secondary uranium minerals. The number of uranyl vanadate mineral species does not reach even 20, and they do not display a large range of structural diversity, but those natural phases form rather massive deposits that can be mined as uranium ores. The number of synthetic uranyl vanadates is three times higher than natural phases, and most of them were obtained using hydrothermal and solid-state techniques. Diversity is also evident in their structural parts. The majority of synthetic compounds, both pure inorganic or organically templated, have their structures based upon mineral-like substructural units of francevillite, uranophane, U₃O₈, and other common topological types, and not even one compound among 57 studied was obtained from simple aqueous solutions at room temperature. This allows us to assume that even under natural conditions, elevated temperatures are required for the formation of isotypic uranyl vanadate minerals, especially in the case of industrially developed thick strata. The structural complexity parameters for natural uranyl vanadates directly depend on the unit cell volume. Keeping in mind that all minerals possess layered structural architecture, it means that structural complexity increases with the increase in the interlayer spacing, which, in turn, depends on the size of cations or water–cationic complexes arranged in the interlayer space. This tendency similarly works for organic molecules, which are incorporated into the uranyl vanadate frameworks. It can also be concluded that the architecture of the uranyl vanadate substructural units defines the complexity of the entire crystal structure. Full article

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16 pages, 4961 KiB

Open AccessArticle

Age Determination of Gem-Quality Green Vanadium Grossular (Var. Tsavorite) from the Neoproterozoic Metamorphic Mozambique Belt, Kenya and Tanzania

by Siyi Zhao, Bo Xu and Yi Zhao

Crystals 2025, 15(1), 9; https://doi.org/10.3390/cryst15010009 - 25 Dec 2024

Viewed by 430

Abstract

Gem-quality garnets, with their high closure temperature (750–800 °C), high transparency, uniform composition, and purity, offer promising prospects for U-Pb dating. Despite decades of recognition that garnets can be dated using the U-Pb method, direct dating remains extremely limited. Tsavorite is a rare [...] Read more.

Gem-quality garnets, with their high closure temperature (750–800 °C), high transparency, uniform composition, and purity, offer promising prospects for U-Pb dating. Despite decades of recognition that garnets can be dated using the U-Pb method, direct dating remains extremely limited. Tsavorite is a rare gem-quality green vanadium-rich grossular hosted in the Neoproterozoic Metamorphic Mozambique Belt (NMMB). Until now, the accurate crystallization age of the tsavorite in Kenya and Lemshuku (Tanzania) has remained unknown. Here, we conducted in situ laser U-Pb geochronological analysis on gem-quality tsavorite samples from Tanzania and Kenya. U-Pb dating of tsavorite sourced from the Lemshuku mine (Tanzania) and the Tsavorite mine (Kenya) yielded ages of 643.9 ± 3.2 Ma and 617.4 ± 4.8 Ma, respectively. The high closure temperature of the U-Pb system within garnets renders it more inclined to preserve crystallization ages rather than documenting cooling events or metamorphic overprinting. Consequently, these ages are indicative of the tsavorite mineralization epochs. These findings align with the most significant metamorphic period documented in the Mozambique Belt, known as the East African Orogen, which occurred between 640 and 600 Ma. U-Pb data have revealed distinct formation times for each district. Dating specific deposits can provide more precise information about the origin of tsavorite, rather than solely relying on isotope or trace element data that have long been used for provenance studies of tsavorite. Full article

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27 pages, 8131 KiB

Open AccessArticle

Formation Conditions of Unusual Extremely Reduced High-Temperature Mineral Assemblages in Rocks of Combustion Metamorphic Complexes

by Igor S. Peretyazhko and Elena A. Savina

Crystals 2024, 14(12), 1052; https://doi.org/10.3390/cryst14121052 - 3 Dec 2024

Viewed by 696

Abstract

New data, including Raman spectroscopy, characterize unusual mineral assemblages from rocks of the Naylga and Khamaryn–Khyral–Khiid combustion metamorphic complexes in Mongolia. Several samples of melilite–nepheline paralava and other thermally altered (metamorphosed) sedimentary rocks contain troilite (FeS), metallic iron Fe⁰, kamacite α-(Fe,Ni) [...] Read more.

New data, including Raman spectroscopy, characterize unusual mineral assemblages from rocks of the Naylga and Khamaryn–Khyral–Khiid combustion metamorphic complexes in Mongolia. Several samples of melilite–nepheline paralava and other thermally altered (metamorphosed) sedimentary rocks contain troilite (FeS), metallic iron Fe⁰, kamacite α-(Fe,Ni) or Ni-bearing Fe⁰, taenite γ-(Fe,Ni) or Ni-rich Fe⁰, barringerite or allabogdanite Fe₂P, schreibersite Fe₃P, steadite Fe₄P = eutectic α-Fe + Fe₃P, wüstite FeO, and cohenite Fe₃C. The paralava matrix includes a fragment composed of magnesiowüstite–ferropericlase (FeO–MgO solid solution), as well as of spinel (Mg,Fe)Al₂O₄ and forsterite. The highest-temperature mineral assemblage belongs to a xenolithic remnant, possibly Fe-rich sinter, which is molten ash left after underground combustion of coal seams. The crystallization temperatures of the observed iron phases were estimated using phase diagrams for the respective systems: Fe–S for iron sulfides and Fe–P ± C for iron phosphides. Iron monosulfides (high-temperature pyrrhotite) with inclusions of Fe⁰ underwent solid-state conversion into troilite at 140 °C. Iron phosphides in inclusions from the early growth zone of anorthite–bytownite in melilite–nepheline paralava crystallized from <1370 to 1165 °C (Fe₂P), 1165–1048 °C (Fe₃P), and <1048 °C (Fe₄P). Phase relations in zoned spherules consisting of troilite +Fe⁰ (or kamacite + taenite) +Fe₃P ± (Fe₃C, Fe₄P) reveal the potential presence of a homogeneous Fe–S–P–C melt at T~1350 °C, which separated into two immiscible melts in the 1350–1250 °C range; namely, a dense Fe–P–C melt in the core and a less dense Fe–S melt in the rim. The melts evolved in accordance with cooling paths in the Fe–S and Fe–P–C phase diagrams. Cohenite and schreibersite in the spherules crystallized between 988 °C and 959 °C. The crystallization temperatures of minerals were used to reconstruct redox patterns with respect to the CCO, IW, IM, and MW buffer equilibria during melting of marly limestone and subsequent crystallization and cooling of melilite–nepheline paralava melts. The origin of the studied CM rocks was explained in a model implying thermal alteration of low-permeable overburden domains in reducing conditions during wild subsurface coal fires, while heating was transferred conductively from adjacent parts of ignited coal seams. The fluid (gas) regime in the zones of combustion was controlled by the CCO buffer at excess atomic carbon. Paralava melts exposed to high-temperature extremely reducing conditions contained droplets of immiscible Fe–S–P–C, Fe–S, Fe–P, and Fe–P–C melts, which then crystallized into reduced mineral assemblages. Full article

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18 pages, 4775 KiB

Open AccessReview

Clay-Based Materials for Heavy Metals Adsorption: Mechanisms, Advancements, and Future Prospects in Environmental Remediation

by Pengsheng Wang, Xinkai Shen, Shusheng Qiu, Long Zhang, Yanping Ma and Jinbao Liang

Crystals 2024, 14(12), 1046; https://doi.org/10.3390/cryst14121046 - 30 Nov 2024

Viewed by 1307

Abstract

Given the severe threats posed by heavy metal pollution to ecological environments and human health, developing effective remediation technologies is of paramount importance. This review delves into the mechanisms, recent advancements, and future prospects of clay mineral-based materials in the adsorption of heavy [...] Read more.

Given the severe threats posed by heavy metal pollution to ecological environments and human health, developing effective remediation technologies is of paramount importance. This review delves into the mechanisms, recent advancements, and future prospects of clay mineral-based materials in the adsorption of heavy metals. Clay minerals such as kaolinite, montmorillonite, and bentonite have demonstrated immense potential for the removal of heavy metals from water and soil due to their natural abundance, low cost, and high efficiency. This article summarizes the latest advancements in the adsorption of heavy metals like chromium, copper, lead, cadmium, arsenic and hydrargyrum by clay minerals, while examining how chemical and physical modifications can enhance the adsorption capacity, selectivity, and stability of these minerals. Furthermore, this review discusses how factors such as pH, temperature, and ionic strength affect adsorption efficiency and outlines challenges and future research directions for optimizing clay-based adsorbents in environmental applications. Full article

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20 pages, 20721 KiB

Open AccessArticle

Investigating Exchange Efficiencies of Sodium and Magnesium to Access Lithium from β-Spodumene and Li-Stuffed β-Quartz (γ-Spodumene)

by Joanne Gamage McEvoy, Yves Thibault and Dominique Duguay

Crystals 2024, 14(11), 988; https://doi.org/10.3390/cryst14110988 - 16 Nov 2024

Viewed by 733

Abstract

After the high-temperature pretreatment of α-spodumene to induce a phase transition to β-spodumene, a derivative of the silica polymorph keatite, often coexisting with metastable Li-stuffed β-quartz (γ-spodumene)_, the conventional approach to access lithium is through ion exchange with hydrogen using concentrated sulfuric [...] Read more.

After the high-temperature pretreatment of α-spodumene to induce a phase transition to β-spodumene, a derivative of the silica polymorph keatite, often coexisting with metastable Li-stuffed β-quartz (γ-spodumene)_, the conventional approach to access lithium is through ion exchange with hydrogen using concentrated sulfuric acid, which presents drawbacks associated with the production of low-value leaching residues. As sodium and magnesium can produce more interesting aluminosilicate byproducts, this study investigates Na⁺ ↔ Li⁺ and Mg²⁺ ↔ 2 Li⁺ substitution efficiencies in β-spodumene and β-quartz. Thermal annealing at 850 °C of the LiAlSi₂O₆ silica derivatives mixed with an equimolar proportion of Na endmember glass of equivalent stoichiometry (NaAlSi₂O₆) indicates that sodium incorporation in β-quartz is limited, whereas the main constraint for not attaining complete growth to a Na_0.5Li_0.5AlSi₂O₆ β-spodumene solid solution is co-crystallization of minor nepheline. For similar experiments in the equimolar LiAlSi₂O₆-Mg_0.5AlSi₂O₆ system, the efficient substitution of Mg for Li is observed in both β-spodumene and β-quartz, consistent with the alkaline earth having an ionic radius closer to lithium than sodium. Ion exchange at lower temperatures was also evaluated by exposing coexisting β-spodumene and β-quartz to molten salts. In NaNO₃ at 320 °C, sodium for lithium exchange reaches ≈90% in β-spodumene but less than ≈2% in β-quartz, suggesting that to be an efficient lithium recovery route, the formation of β-quartz during the conversion of α-spodumene needs to be minimized. At 525 °C in a molten MgCl₂/KCl medium, although full LiAlSi₂O₆-Mg_0.5AlSi₂O₆ solid solution is observed in β-quartz, structural constraints restrict the incorporation of magnesium in β-spodumene to a Li_0.2Mg_0.4AlSi₂O₆ stoichiometry, limiting lithium recovery to 80%. Full article

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18 pages, 6573 KiB

Open AccessArticle

Preliminary Spectroscopic Observations of Marble-Hosted Rubies, Marginal Host Marbles, and Transition Zones Between Marbles and Rubies on Samples from Afghanistan, Myanmar, and Pakistan

by Chen Fan, Yung-Chin Ding and Wing-Tak Lui

Crystals 2024, 14(11), 985; https://doi.org/10.3390/cryst14110985 - 15 Nov 2024

Viewed by 708

Abstract

This study focusses on the spectroscopic observation of marbles, rubies and the transition zone between ruby and its hosted marble that may distinguish the origin of ruby. Samples of ruby-bearing marble were obtained from Afghanistan, Myanmar, and Pakistan. Energy-dispersive X-ray fluorescence was used [...] Read more.

This study focusses on the spectroscopic observation of marbles, rubies and the transition zone between ruby and its hosted marble that may distinguish the origin of ruby. Samples of ruby-bearing marble were obtained from Afghanistan, Myanmar, and Pakistan. Energy-dispersive X-ray fluorescence was used to analyze the chemical compositions. Although the content of other elements in the marble varied with the origin, the Cl content was quite constant. A diagram of the trace elements Fe and Ga was used to determine the origins of the marble-hosted rubies. X-ray diffraction was used to verify the structure phases, where trioctahedral mica, plagioclase, quartz, and alkali feldspar were found in marbles. Ultraviolet–visible spectrophotometry was used for rubies, where a 659 nm fluoresce peak was found in the Myanmar ruby sample, which could make Myanmar ruby redder and more sought after. The bonding of elements and inclusions of the samples were analyzed using Fourier transform infrared spectroscopy, Raman spectroscopy, and photoluminescence. A FTIR peak at 630 cm⁻¹ is found to be useful in judging the temperature of ruby formation. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to analyze the variation of the transition zone, which revealed that the boundary was a gradation zone. Concentrations of Al₂0₃ increased in this zone, but CaCO₃ concentrations decreased. Full article

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24 pages, 3749 KiB

Open AccessArticle

Complex Coacervates: From Polyelectrolyte Solutions to Multifunctional Hydrogels for Bioinspired Crystallization

by Dominik Gruber, Cristina Ruiz-Agudo, Ashit Rao, Simon Pasler, Helmut Cölfen and Elena V. Sturm

Crystals 2024, 14(11), 959; https://doi.org/10.3390/cryst14110959 - 2 Nov 2024

Viewed by 1404

Abstract

Hydrogels represent multifarious functional materials due to their diverse ranges of applicability and physicochemical properties. The complex coacervation of polyacrylate and calcium ions or polyamines with phosphates has been uncovered to be a fascinating approach to synthesizing of multifunctional physically crosslinked hydrogels. To [...] Read more.

Hydrogels represent multifarious functional materials due to their diverse ranges of applicability and physicochemical properties. The complex coacervation of polyacrylate and calcium ions or polyamines with phosphates has been uncovered to be a fascinating approach to synthesizing of multifunctional physically crosslinked hydrogels. To obtain this wide range of properties, the synthesis pathway is of great importance. For this purpose, we investigated the entire mechanism of calcium/polyacrylate, as well as phosphate/polyamine coacervation, starting from early dynamic ion complexation by the polymers, through the determination of the phase boundary and droplet formation, up to the growth and formation of thermodynamically stable macroscopic coacervate hydrogels. By varying the synthesis procedure, injectable hydrogels, as well as plastic coacervates, are presented, which cover a viscosity range of three orders of magnitude. Furthermore, the high calcium content of the calcium/polyacrylate coacervate (~19 wt.%) enables the usage of those coacervates as an ions reservoir for the formation of amorphous and crystalline calcium-containing salts like calcium carbonates and calcium phosphates. The exceptional properties of the coacervates obtained here, such as thermodynamic stability, viscosity/plasticity, resistance to acids, and adhesive strength, combined with the straightforward synthesis and the character of an ions reservoir, open a promising field of bioinspired composite materials for osteology and dentistry. Full article

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15 pages, 4943 KiB

Open AccessArticle

In-Depth Characterization of Natural Clays from Southeast Albania

by Altin Mele, Viviana Scognamiglio, Valeria Nocerino, Luca De Stefano, Arben Memo, Roberta G. Toro, Manuela Rossi, Francesco Baldassarre and Francesco Capitelli

Crystals 2024, 14(10), 903; https://doi.org/10.3390/cryst14100903 - 18 Oct 2024

Viewed by 1040

Abstract

Clays have been exploited in the manufacture of diverse products from ceramics to paints, pharmaceuticals, plastics, cosmetics, and more. Thus, they can be used in many industrial applications, showing good adsorbent ability thanks to their lamellar structure, high cation exchange capacity, pore size [...] Read more.

Clays have been exploited in the manufacture of diverse products from ceramics to paints, pharmaceuticals, plastics, cosmetics, and more. Thus, they can be used in many industrial applications, showing good adsorbent ability thanks to their lamellar structure, high cation exchange capacity, pore size distribution, and large surface area. For this reason, considerable attention has been paid to their in-depth characterization, for further integration in sectors such as biomedicine, construction, remediation, aerospace, and nanotechnology. For this aim, two samples of natural clays, ALO1 and PRE4, from the southeast part of Albania, were subject to a multi-methodological characterization, with the aim of addressing the use of such geomaterials in possible sensing applications. X-ray fluorescence analysis, morphological characterization of the samples, and energy-dispersive system spectroscopy pointed to an extreme mineralogical variety, with kaolinite in AL01 and montmorillonite in PRE4 as the most abundant phases. This fact was further confirmed by powder X-ray diffraction, showing a quartz content of 20%, a kaolinite content of 64%, and a muscovite content of 16% for ALO1; meanwhile, for PRE4, we found a content of quartz of 45%, a content of montmorillonite of 34.9%, and a content of clinochlore of 20%. Infrared spectroscopy and thermal analyses confirmed the presence of hydroxyl groups in both samples, suggesting a higher content in ALO1. Measurement of N₂ adsorption isotherms on the clay samples yields specific surface areas of 87 m²/g for PRE4 and 32 m²/g for ALO1, pore volumes of 0.721 cm³/g for PRE4 and 0.637 cm³/g for ALO1, and similar pore sizes in the range of 6–12 nm. Electrochemical analysis highlighted a good conductivity of ALO1 and PRE4 when used for the modification of commercial carbon-based screen-printed electrodes. In detail, higher currents were registered by differential pulse voltammetry for the electrodes modified with the clays with respect to bare electrodes, as well as good repeatability of the measurements. In addition, a comparative study with nanomaterials, known for their good conductivity, was achieved, using carbon black and gold nanoparticles as a reference, showing that the conductivity of the clays was lower than but not so different from those of the reference materials. Full article

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17 pages, 6359 KiB

Open AccessArticle

Chemical Composition and Spectral Variation in Gem-Quality Blue Iron-Bearing Tourmaline from Brazil

by Yifang Chen, Duo Xu, Zhengyu Zhou, Dietmar Schwarz, Junhao Zheng and Lingmin Zhang

Crystals 2024, 14(10), 877; https://doi.org/10.3390/cryst14100877 - 4 Oct 2024

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Abstract

This study, conducted a spectroscopic analysis of 10 gem-quality blue tourmaline samples from Minas Gerais, Brazil, focused on detailed variations in their infrared, Raman, and UV-VIS spectra. Conventional gemological tests, electron-probe microanalysis, infrared spectroscopy (mid- and near-infrared), Raman spectroscopy, and UV-visible spectroscopy were [...] Read more.

This study, conducted a spectroscopic analysis of 10 gem-quality blue tourmaline samples from Minas Gerais, Brazil, focused on detailed variations in their infrared, Raman, and UV-VIS spectra. Conventional gemological tests, electron-probe microanalysis, infrared spectroscopy (mid- and near-infrared), Raman spectroscopy, and UV-visible spectroscopy were used to systematically analyze the chemical composition and spectral characteristics of the samples. The infrared spectra revealed vibrations of [YO₆], [TO₄], [BO₃], [OH], and H₂O groups, indicating different bonding profiles, with the [OH] vibrational frequency showing a direct correlation with FeO and MnO content. The Raman spectra primarily reflected the stretching vibrations of metal–oxygen bonds and hydroxyl groups, indicating the complexity of the local environment in the crystal structure. The UV-VIS spectra showed that the broad absorption band around 725 nm was due to intermetallic charge transfer between Fe²⁺ and Fe³⁺. This work provides new insights into the local bonding environment within the crystal structure by providing precise spectral data of natural blue tourmaline, and a more accurate classification and evaluation of blue tourmaline through fine spectral change characteristics related to crystal chemistry has important implications for both academic research and the gemstone industry. Full article

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17 pages, 11981 KiB

Open AccessArticle

The Enamelled Tiles of Olite’s Castle (Spain): Characterization, Provenance, and Manufacture Technology

by Iván Ruiz-Ardanaz, Esther Lasheras and Adrián Durán

Crystals 2024, 14(9), 813; https://doi.org/10.3390/cryst14090813 - 14 Sep 2024

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Abstract

The objective of this study was to determine the authorship, provenance, and technology of the mudejar enamelled tiles from the Olite Castle (northern Spain, 14th century). According to previous knowledge, Olite’s enamelled tiles had been manufactured in Manises (Valencia, Spain). The analysis of [...] Read more.

The objective of this study was to determine the authorship, provenance, and technology of the mudejar enamelled tiles from the Olite Castle (northern Spain, 14th century). According to previous knowledge, Olite’s enamelled tiles had been manufactured in Manises (Valencia, Spain). The analysis of ceramic pastes revealed the existence of two different chemical compositions, suggesting the use of two different clay sources, probably one from the Tudela area, and another from the Tafalla–Olite area. Those probably made in the Tudela area stood out with a higher diopside (CaMgSi₂O₆) content. Those probably made in the Tafalla–Olite area stood out for their calcium-bearing minerals, such as calcite (CaCO₃) or gehlenite (Ca₂Al(AlSi)O₇). On this basis, production in Manises has been ruled out. However, it is highly probable that the artisans of Manises would have led the production from Tudela. The study of the firing temperatures and composition of the enamels indicated that the production methods and materials used in Tafalla–Olite (800–850 °C) and Tudela (higher than 900 °C) were different, reflecting the influence of local and Manises artisans, respectively. In Olite tiles, enamel was applied following recipes from the 14th and 15th centuries. Full article

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18 pages, 4122 KiB

Open AccessArticle

Crystallization of Calcium Carbonate and Calcium Phosphate Phases in Silica Hydrogel: Morphological and Compositional Characterization

by Nuria Sánchez-Pastor, André Jorge Pinto, Pablo del Buey Fernández and José Manuel Astilleros

Crystals 2024, 14(7), 635; https://doi.org/10.3390/cryst14070635 - 10 Jul 2024

Viewed by 1410

Abstract

The present study showcases a series of crystallization experiments using a specially designed double diffusion system to grow crystals belonging to the calcium carbonate–phosphate system. The experimental U-shaped device comprised two vertical solution containers, separated by a horizontal column of silica hydrogel. Each [...] Read more.

The present study showcases a series of crystallization experiments using a specially designed double diffusion system to grow crystals belonging to the calcium carbonate–phosphate system. The experimental U-shaped device comprised two vertical solution containers, separated by a horizontal column of silica hydrogel. Each container was filled with 0.5 M CaCl₂ and 0.5 M Na₂CO₃ solutions, which diffused through the gel column over time. Na₃PO₄ solutions, with 50 and 500 ppm concentrations, were incorporated into the gel in different experiments, resulting in a homogeneous distribution of phosphate concentrations within the diffusion column. After 15- and 30-day incubation periods post-nucleation, the crystals formed in different sections of the gel were carefully extracted and studied with scanning electron microscopy and electron microprobe. Additionally, Raman spectra were collected from the samples using a confocal Raman microscope, providing further insights into their molecular composition and structural properties. The obtained results show that under the induced experimental conditions (i) phosphate incorporates into calcite’s structure, and (ii) the growth of calcium phosphates in the presence of carbonate ions involves the sequential, heterogeneous nucleation of CO₃-bearing OCP/HAP-like phases, with Raman spectral characteristics very similar to those of bioapatites. Full article

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