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Influence of grain size and plastic deformation on the phase transformation of enstatite: insights from microstructures produced during the back-transformation of protoenstatite to clinoenstatite 晶粒尺寸和塑性变形对恩氏铁锂辉石相变的影响:从原恩氏铁锂辉石向克氏铁锂辉石逆变过程中产生的微观结构中获得的启示
IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2024-08-05 DOI: 10.1007/s00269-024-01294-5
Miki Tasaka, Maya Iwago

Enstatite (Mg2Si2O6) is a member of the pyroxene group and an important mineral in the lower crust and upper mantle. Enstatite has three phases at ambient pressure: protoenstatite, orthoenstatite, and clinoenstatite. Previously, the polymorphic transformation of pyroxene has been characterized using bulk techniques such as X-ray diffraction of powders. Given that rocks are crystal aggregates, it is important to use aggregates to understand phase transformations. We therefore conducted grain growth and deformation experiments using aggregates of enstatite to investigate phase transformations. Grain growth experiments were conducted at temperatures (T) of 1345 and 1360 °C under a vacuum of ≈ 10 Pa using an alumina tube furnace. Deformation experiments were conducted at T = 1310 °C and room pressure, a strain rate of ≈ 10–4 s–1, and a resulting stress of ≈ 150 MPa. The samples were analyzed using a scanning electron microscope, electron backscatter diffraction (EBSD), and X-ray diffraction. The results indicate that the grain size affects the transformation from protoenstatite to clinoenstatite, whereas deformation by diffusion creep does not. The EBSD analyses show that the volume fraction of clinoenstatite increases with increasing grain size. The samples underwent diffusion creep during the deformation experiments, and there were no distinct microstructural differences between deformed and undeformed samples. The EBSD analyses show that the transformed clinoenstatite has a characteristic twin structure with a misorientation angle of 180° and a rotation axis of [100] or [001]. Grain sizes become smaller during the phase transformation, even if the mechanism can be characterized as a second-order transformation.

黝帘石(Mg2Si2O6)是辉石类的一种,也是下地壳和上地幔中的一种重要矿物。在常压下,恩氏闪长岩有三相:原恩氏闪长岩、正恩氏闪长岩和克利诺恩氏闪长岩。以前,人们使用粉末的 X 射线衍射等大块技术来描述辉石的多晶体转变。鉴于岩石是晶体聚集体,利用聚集体来了解相变非常重要。因此,我们利用辉石聚集体进行了晶粒生长和变形实验,以研究相变。晶粒生长实验是在 1345 和 1360 °C 的温度(T)下,利用氧化铝管式炉在≈ 10 Pa 的真空条件下进行的。变形实验是在 T = 1310 °C 和室压下进行的,应变速率为 ≈ 10-4 s-1,产生的应力为 ≈ 150 MPa。使用扫描电子显微镜、电子反向散射衍射(EBSD)和 X 射线衍射对样品进行了分析。结果表明,晶粒尺寸会影响原芒硝向克氏芒硝的转变,而扩散蠕变变形则不会。EBSD 分析表明,随着晶粒尺寸的增大,闪长岩的体积分数也随之增大。样品在变形实验过程中发生了扩散蠕变,变形样品和未变形样品之间没有明显的微观结构差异。EBSD 分析表明,转变后的闪长岩具有特征性的孪晶结构,错向角为 180°,旋转轴为 [100] 或 [001]。在相变过程中,晶粒尺寸变小,即使其机理可定性为二阶转变。
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引用次数: 0
Crystallographic mechanism of the elastic behaviour of synthetic bütschliite K2Ca(CO3)2 on compression to 20 GPa 压缩至 20 GPa 时合成菱镁矿 K2Ca(CO3)2 弹性行为的晶体学机制
IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2024-07-28 DOI: 10.1007/s00269-024-01291-8
Anna Yu. Likhacheva, Alexandr V. Romanenko, Sergey V. Rashchenko, Sofija Miloš, Paolo Lotti, Ronald Miletich, Anton Shatskiy

Bütschliite, K2Ca(CO3)2, occurring as inclusions in mantle minerals, is regarded as one of the key phases to understand phase relationships of dense potassium carbonates and thus to evaluate their potential role within the Earth’s deep carbon cycle. Accordingly, the high-pressure behavior of synthetic bütschliite has been investigated by in-situ single-crystal X-ray diffraction under isothermal compression up to 20 GPa at T = 298 K. The compression mechanism before and after the trigonal-to-monoclinic (R-3m to C2/m) phase transition at ∼6 GPa, found previously, is characterized in terms of the evolution of the cation polyhedra and carbonate groups. On this basis, the modulation of the axial compression is interpreted, and the contribution of the cation polyhedra into the bulk compression is estimated. The refined compressibility of the monoclinic phase (K0 = 44(2) GPa) fits to the trend of the carbonate bulk modulus versus average non-carbon cation radius. The analysis of the obtained and literature structural data suggests the distortion of a large cation polyhedron to be an effective tool to strengthen the carbonate structure at high pressure. On the other hand, the observed symmetrization of the cation polyhedra in trigonal bütschliite is apparently a crucial factor of its stabilization at high pressure upon the temperature rise observed previously. The structural crystallography provided in this study supports the enhanced stability of trigonal bütschliite at high P, T conditions and its significance of being considered as a constituent of the inclusions in deep minerals.

作为地幔矿物中的包裹体出现的黑钾石(K2Ca(CO3)2)被认为是了解致密碳酸钾相关系并进而评估其在地球深层碳循环中潜在作用的关键相位之一。因此,我们通过原位单晶 X 射线衍射研究了合成黑钾盐在 20 GPa 等温压缩(T = 298 K)条件下的高压行为。我们从阳离子多面体和碳酸酯基团的演化来描述了之前发现的在 6 GPa ∼时三方到单斜(R-3m 到 C2/m)相变前后的压缩机制。在此基础上,对轴向压缩的调制进行了解释,并估算了阳离子多面体对体积压缩的贡献。单斜相(K0 = 44(2) GPa)的细化压缩性与碳酸盐体积模量与非碳阳离子平均半径的趋势相吻合。对获得的结构数据和文献数据的分析表明,大阳离子多面体的变形是在高压下强化碳酸盐结构的有效工具。另一方面,所观察到的三方绿柱石中阳离子多面体的对称性显然是其在高压下稳定的关键因素,而这正是之前所观察到的温度升高的原因。本研究提供的结构晶体学支持了三方菱锰矿在高P、高T条件下稳定性的增强,以及将其视为深矿物中包裹体成分的重要意义。
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引用次数: 0
High-pressure structural behavior of α-K2Ca3(CO3)4 up to 20 GPa 高达 20 GPa 的 α-K2Ca3(CO3)4 高压结构行为
IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2024-07-28 DOI: 10.1007/s00269-024-01292-7
Mark A. Ignatov, Sergey V. Rashchenko, Anna Yu Likhacheva, Alexandr V. Romanenko, Anton F. Shatskiy, Anton V. Arefiev, Konstantin D. Litasov

K-Ca double carbonates recently identified in inclusions in diamonds, as well as associated alkali-carbonate melts can play an important role in the deep carbon cycle. We studied pressure-induced changes in the crystal structure of high-pressure α-K2Ca3(CO3)4 phase up to 20 GPa using synchrotron single-crystal x-ray diffraction in diamond anvil cell. At ~ 7 GPa at room temperature the orthorhombic P212121 phase of α-K2Ca3(CO3)4 undergoes displacive phase transition into monoclinic P1121 phase. Despite the phase transition, PV-curve does not demonstrate any irregularities so that both phases can be described by the same 4th order Birch-Murnaghan equation of state with V0 = 1072.5(3) Å3, K0 = 51.1(8) GPa, K0=3.7(3), K’’0=0.12(6).

最近在金刚石包裹体中发现的 K-Ca 双碳酸盐以及相关的碱碳酸盐熔体在深层碳循环中扮演着重要角色。我们利用同步辐射单晶 X 射线衍射技术,在金刚石砧槽中研究了高达 20 GPa 的高压 α-K2Ca3(CO3)4 相晶体结构的压力诱导变化。在室温约 7 GPa 时,α-K2Ca3(CO3)4 的正交 P212121 相发生位移相变,变成单斜 P1121 相。尽管发生了相变,但 PV 曲线并未显示出任何不规则性,因此这两种相可以用相同的四阶 Birch-Murnaghan 状态方程来描述:V0 = 1072.5(3) Å3,K0 = 51.1(8) GPa,K'0=3.7(3),K''0=0.12(6)。
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引用次数: 0
New insight into the phase transition and kinetics of the dehydroxylation of bulk-to-nano chrysotile 大块温石棉到纳米温石棉脱羟基的相变和动力学新见解
IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2024-07-23 DOI: 10.1007/s00269-024-01288-3
Jifa Long, Wentao Liu, Ningbo Zhang, Hanting Zhang, Qi Xiao, Suping Huang

In this work, the self-made chrysotile fiber membrane (CFM) and raw chrysotile fiber (CF) were calcined in air from 500 to 800 °C. The XRD pattern of CFM showed that the diffraction peak of chrysotile weakened when the temperature was from room temperature to 550 °C, and CFM had a shorter amorphous interval at 600–700 °C. While, no amorphous phase appeared in CF during calcination, and forsterite begined to appear at 650 °C. SEM images showed that CFM could still maintain the integrity of the network structure at 600–800 °C, while CF gradually melted into coarse fiber bundles with the increase of calcination temperature, and sintering traces appeared. After that,the kinetics of the dehydroxylation of chrysotile in CFM and CF was studied. The dehydroxylation of CFM is a one-step reaction, the calculated activation energy is 243.33 kJ mol−1, which conforms to the two-dimensional ‘Valensi’ model with mechanism function G(α) = (1−α)ln(1−α) + α. The dehydroxylation of CF is divided into two stages, the activation energy are 222.87 kJ mol−1 and 316.04 kJ mol−1. The first stage of CF conforms to two-dimensional ‘Jander’ model (n = 2) with mechanism function G(α) = [1−(1−α)1/2]2, the second stage of CF conforms to the random nucleation and subsequent growth ‘Avrami-Erofeev’ model (n = 3/2) with mechanism function G(α) = [−ln(1−α)]2/3.

在这项工作中,自制的温石棉纤维膜(CFM)和温石棉原纤维(CF)在空气中进行了500至800 °C的煅烧。CFM 的 XRD 图谱显示,当温度从室温升至 550 ℃ 时,温石棉的衍射峰减弱,在 600-700 ℃ 时,CFM 的无定形间隔缩短。而 CF 在煅烧过程中没有出现无定形相,在 650 ℃ 时开始出现绿柱石。扫描电镜图像显示,CFM 在 600-800 ℃ 时仍能保持网络结构的完整性,而 CF 则随着煅烧温度的升高逐渐熔化成粗纤维束,并出现烧结痕迹。随后,研究了温石棉在 CFM 和 CF 中的脱羟动力学。CFM 的脱羟基反应为一步反应,计算的活化能为 243.33 kJ mol-1,符合二维 "Valensi "模型,机理函数为 G(α) = (1-α)ln(1-α) + α。CF 的脱羟基反应分为两个阶段,活化能分别为 222.87 kJ mol-1 和 316.04 kJ mol-1。CF 的第一阶段符合二维 "扬德 "模型(n = 2),机理函数 G(α) = [1-(1-α)1/2]2 ;CF 的第二阶段符合随机成核和后续生长的 "阿夫拉米-埃罗费耶夫 "模型(n = 3/2),机理函数 G(α) = [-ln(1-α)]2/3。
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引用次数: 0
Theoretical infrared signature of OH defects in Fe3+, Cr3+ and Al3+-doped enstatite 掺杂 Fe3+、Cr3+ 和 Al3+ 的芒硝中 OH 缺陷的理论红外特征
IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2024-07-20 DOI: 10.1007/s00269-024-01289-2
Etienne Balan, Jannick Ingrin

The infrared spectroscopic properties of selected defects involving one proton and one nearby M3+ (M = Al, Cr, Fe) substitution in orthoenstatite are investigated by first-principles calculations. Based on the theoretical results, the absorption bands experimentally observed on synthetic samples with high crystalline quality and low doping levels can be assigned to specific defect configurations. Most of them correspond to Mg vacancies at M2 sites locally compensated by one proton and one M3+ cation at a nearby M1 site. This confirms that the M3+ + H+ = 2 Mg2+ exchange mechanism is the dominant hydrogen incorporation mechanism at the lowest concentration levels in doped enstatite. At higher concentration levels, more complex incorporation mechanisms could become dominant in Al-bearing samples.

通过第一原理计算,研究了正沸石中涉及一个质子和一个邻近 M3+(M = Al、Cr、Fe)取代的选定缺陷的红外光谱特性。根据理论结果,在结晶质量高、掺杂水平低的合成样品上实验观察到的吸收带可归属于特定的缺陷构型。它们大多对应于 M2 位点上的镁空位,由附近 M1 位点上的一个质子和一个 M3+ 阳离子局部补偿。这证实了 M3+ + H+ = 2 Mg2+ 交换机制是掺杂磷灰石中最低浓度水平的主要氢掺入机制。当浓度水平较高时,更复杂的掺入机制可能会在含铝样品中占据主导地位。
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引用次数: 0
Pressure–volume equation of state of Fe18Pt82 Fe18Pt82 的压力-体积状态方程
IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2024-07-20 DOI: 10.1007/s00269-024-01275-8
Meryem Berrada, Siheng Wang, Bin Chen, Vitali Prakapenka, Stella Chariton, Marc M. Hirschmann, Jie Li

Platinum-iron (Pt-Fe) alloys have long served as oxygen fugacity sensors in high-temperature experiments investigating Earth and planetary interiors, relying on the equilibrium between Fe within the alloy and FeO in coexisting oxides or silicates. Despite their significance, studies on intermediate compositions remain limited. This investigation focuses on compressibility of Fe18Pt82 up to (sim) 40 GPa at ambient temperature and explores the pressure-dependent characteristics of the oxygen fugacity relationship. In-situ X-ray diffraction measurements confirm the stability of the fcc phase in Fe18Pt82 across the pressure range. The fit to the compression data by the third-order Birch–Murnaghan equation of state results in ({V}_{0}=59.14 pm 0.08)Å3, ({K}_{0}=266 pm 13) GPa, and ({K}_{0}^{prime}=4.7 pm 0.7). The differences between this fit and the Vinet and Kunc equations of state fall within the range of uncertainty. Comparing results with reported data for other Pt-Fe alloys reveals a nearly linear trend between volume and the Fe content in Pt-Fe alloys at ambient pressure. Unlike more iron-rich alloys, the excess volume of mixing of Fe18Pt82 ((sim) 0.21 cm3/mol) remains nearly constant across the examined pressure range. Estimates of the excess Gibbs free energy suggest diminishing non-ideal contributions to thermodynamic activities as pressure increases.

长期以来,铂-铁(Pt-Fe)合金一直是研究地球和行星内部的高温实验中的氧逸散传感器,它依赖于合金中的铁与共存氧化物或硅酸盐中的氧化铁之间的平衡。尽管中间成分非常重要,但对它们的研究仍然有限。这项研究的重点是 Fe18Pt82 在环境温度下达到 40 GPa 时的可压缩性,并探索了氧逸散关系随压力变化的特征。原位 X 射线衍射测量证实了 Fe18Pt82 的 fcc 相在整个压力范围内的稳定性。三阶伯奇-默纳汉状态方程对压缩数据的拟合结果为:({V}_{0}=59.14 pm 0.08)Å3, ({K}_{0}=266 pm 13) GPa, 和({K}_{0}^{prime}=4.7 pm 0.7)。这一拟合结果与 Vinet 和 Kunc 状态方程之间的差异在不确定范围之内。将结果与其他铂铁合金的报告数据进行比较,可以发现在常压下,铂铁合金的体积与铁含量之间几乎呈线性趋势。与更多的富铁合金不同,Fe18Pt82 的过量混合体积(0.21 cm3/mol)在所考察的压力范围内几乎保持不变。对过剩吉布斯自由能的估算表明,随着压力的增加,对热力学活动的非理想贡献会逐渐减小。
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引用次数: 0
Purification mechanism of microcrystalline graphite and dissolution of non-carbon impurity during alkali autoclave-acid leaching 碱高压釜-酸浸出过程中微晶石墨的净化机理和非碳杂质的溶解
IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2024-07-18 DOI: 10.1007/s00269-024-01290-9
Zhang Xiyue, Sun Hongjuan, Peng Tongjiang, Zeng Li, Liu Bo

Low impurity content is crucial for graphite applications and microcrystalline graphite is an important candidate material. In this study, natural microcrystalline graphite, with a fixed carbon content of 76.65%, was purified by an alkaline autoclave-acid leaching method. The effects of the mole ratio of NaOH to Si and Al in graphite, the liquid–solid ratio of NaOH solution and graphite, alkali autoclave temperature and reaction time on the purity of microcrystalline graphite were studied. Results showed that the dissolution and phase transformation of non-carbon impurities were closely related to the purification process. During the alkali autoclave stage, complete dissolution of quartz was observed. The Si–O tetrahedra and Al–O octahedra structures in aluminosilicate minerals were damaged and [Al (OH)4], [H2SiO4]2− and [SiO2 (OH)3] were released. The soluble silicate and aluminate ions underwent recrystallization, producing cancrinite and sodalite that could be dissolved by acid leaching, resulting in purified microcrystalline graphite. The purity of microcrystalline graphite was further improved due to the autoclave treatment allowed NaOH solution to penetrate into the cracks of microcrystalline graphite aggregates under high pressure. In addition, the acid solution could enter the micropores left by alkali etching to dissolve the residual impurities. The fixed carbon content of microcrystalline graphite could be increased to 99.9% through the alkaline autoclave-acid leaching method.

Graphical abstract

低杂质含量对石墨的应用至关重要,而微晶石墨是一种重要的候选材料。本研究采用碱性高压釜-酸浸法提纯了固定碳含量为 76.65% 的天然微晶石墨。研究了 NaOH 与石墨中 Si 和 Al 的摩尔比、NaOH 溶液与石墨的液固比、碱高压釜温度和反应时间对微晶石墨纯度的影响。结果表明,非碳杂质的溶解和相变与提纯过程密切相关。在碱高压釜阶段,观察到石英完全溶解。铝硅酸盐矿物中的 Si-O 四面体和 Al-O 八面体结构遭到破坏,[Al (OH)4]-、[H2SiO4]2- 和 [SiO2 (OH)3]- 被释放出来。可溶性硅酸根离子和铝酸根离子发生重结晶,生成可通过酸浸法溶解的硅灰石和钠长石,从而得到纯化的微晶石墨。由于高压釜处理可使 NaOH 溶液在高压下渗入微晶石墨聚集体的裂缝中,因此微晶石墨的纯度进一步提高。此外,酸溶液还能进入碱蚀刻留下的微孔,溶解残留的杂质。通过碱性高压釜-酸浸出法,微晶石墨的固定碳含量可提高到 99.9%。
{"title":"Purification mechanism of microcrystalline graphite and dissolution of non-carbon impurity during alkali autoclave-acid leaching","authors":"Zhang Xiyue,&nbsp;Sun Hongjuan,&nbsp;Peng Tongjiang,&nbsp;Zeng Li,&nbsp;Liu Bo","doi":"10.1007/s00269-024-01290-9","DOIUrl":"10.1007/s00269-024-01290-9","url":null,"abstract":"<div><p>Low impurity content is crucial for graphite applications and microcrystalline graphite is an important candidate material. In this study, natural microcrystalline graphite, with a fixed carbon content of 76.65%, was purified by an alkaline autoclave-acid leaching method. The effects of the mole ratio of NaOH to Si and Al in graphite, the liquid–solid ratio of NaOH solution and graphite, alkali autoclave temperature and reaction time on the purity of microcrystalline graphite were studied. Results showed that the dissolution and phase transformation of non-carbon impurities were closely related to the purification process. During the alkali autoclave stage, complete dissolution of quartz was observed. The Si–O tetrahedra and Al–O octahedra structures in aluminosilicate minerals were damaged and [Al (OH)<sub>4</sub>]<sup>−</sup>, [H<sub>2</sub>SiO<sub>4</sub>]<sup>2−</sup> and [SiO<sub>2</sub> (OH)<sub>3</sub>]<sup>−</sup> were released. The soluble silicate and aluminate ions underwent recrystallization, producing cancrinite and sodalite that could be dissolved by acid leaching, resulting in purified microcrystalline graphite. The purity of microcrystalline graphite was further improved due to the autoclave treatment allowed NaOH solution to penetrate into the cracks of microcrystalline graphite aggregates under high pressure. In addition, the acid solution could enter the micropores left by alkali etching to dissolve the residual impurities. The fixed carbon content of microcrystalline graphite could be increased to 99.9% through the alkaline autoclave-acid leaching method.</p><h3>Graphical abstract</h3>\u0000<div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":20132,"journal":{"name":"Physics and Chemistry of Minerals","volume":"51 3","pages":""},"PeriodicalIF":1.2,"publicationDate":"2024-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141739899","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Atomic resolution transmission electron microscopy visualisation of channel occupancy in beryl in different crystallographic directions 用原子分辨率透射电子显微镜观察绿柱石在不同晶体学方向上的通道占用情况
IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2024-07-05 DOI: 10.1007/s00269-024-01285-6
Carina Silke Hanser, Per Erik Vullum, Antonius Theodorus Johannes van Helvoort, Fabian Dietmar Schmitz, Tobias Häger, Roman Botcharnikov, Bodil Holst

The causes of colour in beryl have been a research topic for decades. For some varieties, such as emerald (green, coloured by Cr3+ and/or V3+), the main cause of colour is substitutions by metal atoms within the framework. However, the causes for the yellow and blue colours in heliodor, golden beryl and aquamarine are still debated. It is generally agreed that Fe ions are responsible for the colour, but there are differing conclusions about the valence states of these ions, the occupied positions and the colour-inducing processes involved. The colour of aquamarine is commonly attributed to intervalence charge transfer (IVCT) between Fe3+ and Fe2+. Various combinations of sites have been proposed to host the Fe ions engaging in this IVCT. Here we present a new approach to address the topic of colour generation: atomic resolution scanning transmission electron microscopy (STEM). For the first time, atomic resolution images of a beryl (natural aquamarine) are presented in the three crystallographic directions [0001], [1-210] and [1-100]. Ions are clearly resolved in the channels. From the ratio of channel occupation and the correlation of the atoms per formula unit (apfu) calculations we conclude that Fe resides in the framework, not in the channels. The projections in the [1-210] direction directly show that the cavity channel site 2a is occupied, most likely by Cs, in agreement with recent results in the literature.

几十年来,绿柱石的颜色成因一直是一个研究课题。对于某些品种,如祖母绿(绿色,由 Cr3+ 和/或 V3+ 着色),颜色的主要成因是框架内金属原子的置换。然而,关于氦碘石、金绿柱石和海蓝宝石中黄色和蓝色的成因仍存在争议。人们普遍认为铁离子是造成颜色的原因,但对这些离子的价态、占据的位置和所涉及的致色过程却有不同的结论。海蓝宝的颜色通常归因于 Fe3+ 和 Fe2+ 之间的间隔电荷转移(IVCT)。人们提出了各种不同的位置组合来承载参与这种 IVCT 的铁离子。在此,我们提出了一种解决颜色生成问题的新方法:原子分辨率扫描透射电子显微镜(STEM)。我们首次展示了绿柱石(天然海蓝宝石)在三个晶体学方向 [0001]、[1-210] 和 [1-100] 上的原子分辨率图像。离子在通道中清晰分辨。根据沟道占据率和每式单位(apfu)原子的相关性计算,我们得出结论:铁存在于框架中,而不是沟道中。[1-210]方向上的投影直接表明,空腔通道位点 2a 被占据,很可能是被铯占据,这与最近的文献结果一致。
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引用次数: 0
The packing fraction of the oxygen sublattice: its impact on the heat of mixing 氧亚晶格的堆积分数:对混合热的影响
IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2024-06-04 DOI: 10.1007/s00269-024-01277-6
Artur Benisek, Edgar Dachs

The heat of mixing of some petrological relevant substitutions (i.e., Mg-Al, Si-Al, Mg-Ti, Mg-Ca, and Mg-Fe) was investigated systematically in silicates, titanates, tungstates, carbonates, oxides, hydroxides, and sulphates by density functional theory calculations (e.g., melilite, chlorite, biotite, brucite, cordierite, amphibole, talc, pseudobrookite, pyroxene, olivine, wadsleyite, ilmenite, MgWO4, ringwoodite (spinel), perovskite, pyrope-grossular, magnesite-calcite, MgO-CaO, anhydrous and different hydrated MgSO4). A specific substitution is characterised by different microscopic interaction energies in different minerals, e.g., the octahedral Mg-Al exchange on a single crystallographic site in pyroxene has a microscopic interaction energy that is more than twice compared to that in biotite. A comparative investigation of the heat of mixing using microscopic interaction energies on a single crystallographic site has the advantage that they are not influenced by cation ordering. They could be successfully correlated with the stiffnesses of the minerals, which in turn were scaled to the oxygen packing fraction, a parameter that is easily available for poorly investigated minerals. With this information, the interaction energies of a certain substitution can be transferred from minerals where they are well-known to mineral groups where they are less- or unknown. Using the cross-site terms and the microscopic interaction energies, the macroscopic interaction energies of the coupled substitution, e.g., Mg + Si = Al + Al, of biotite and pyroxene were calculated, which are, however, affected by cation ordering and different degrees of local charge balance, for which appropriate models are necessary.

通过密度泛函理论计算,系统地研究了硅酸盐、钛酸盐、钨酸盐、碳酸盐、氧化物、氢氧化物和硫酸盐中一些与岩石学有关的置换(即镁铝、硅铝、镁钛、镁钙和镁铁)的混合热(例如,镁铝置换、镁钛置换、镁钙置换和镁铁置换)、梅里来石、绿泥石、黑云母、白云石、堇青石、闪石、滑石、假勃洛克石、辉石、橄榄石、瓦氏石、钛铁矿、MgWO4、环钨矿(尖晶石)、透辉石、辉绿岩-毛玻璃、菱镁矿-钙钛矿、MgO-CaO、无水和不同水合硫酸镁)。特定的置换在不同矿物中具有不同的微观相互作用能,例如,辉石中单个晶体学位点上的八面体镁铝交换的微观相互作用能是黑云母的两倍多。使用单个晶体学位点上的微观相互作用能对混合热进行比较研究,其优点是不受阳离子有序性的影响。它们可以成功地与矿物的刚度相关联,而矿物的刚度又与氧堆积分数成比例,对于研究较少的矿物来说,氧堆积分数是一个很容易获得的参数。有了这些信息,就可以将某种替代物的相互作用能从已知的矿物转移到较少或未知的矿物组中。利用跨位点项和微观相互作用能,计算了耦合置换的宏观相互作用能,例如生物橄榄石和辉石中的 Mg + Si = Al + Al,但这受到阳离子有序化和不同程度的局部电荷平衡的影响,因此需要适当的模型。
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引用次数: 0
On the crystal-chemistry of inderite, Mg[B3O3(OH)5](H2O)4·H2O 关于橄榄石(Mg[B_3O_3(OH)_5](H_2O)_4-H_2O)的晶体化学性质
IF 1.2 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2024-05-23 DOI: 10.1007/s00269-024-01281-w
G. Diego Gatta, Silvia C. Capelli, Davide Comboni, Enrico Cannaò

The crystal chemistry of inderite, a hydrous borate with known ideal formula MgB3O3(OH)5·5H2O from the Kramer deposit, was re-investigated by electron probe micro-analysis in wavelength dispersive mode, laser ablation-(multi collector-)inductively coupled plasma-mass spectrometry and single-crystal neutron diffraction. The chemical data prove that the real composition of the investigated inderite is substantially identical to the ideal one, with insignificant content of potential isomorphic substituents, so that, excluding B, inderite does not contain any other industrially-relevant element (e.g., Li concentration is lower than 2.5 wt ppm, Be or REE lower than 0.1 wt ppm). The average δ11BNIST951 value of ca. − 7 ‰ lies within the range of values in which the source of boron is ascribable to terrestrial reservoirs (e.g., hydrothermal brines), rather than to marine ones. Neutron structure refinements, at both 280 and 10 K, confirm that the building units of the structure of inderite consist of: two BO2(OH)2 tetrahedra (B-ion in sp3 electronic configuration) and one BO2(OH) triangle (B-ion in sp2 electronic configuration), linked by corner-sharing to form a (soroborate) B3O3(OH)5 ring, and a Mg-octahedron Mg(OH)2(OH2)4. The B3O3(OH)5 ring and the Mg-octahedron are connected, by corner-sharing, to form an isolated Mg(H2O)4B3O3(OH)5 (molecular) cluster. The tri-dimensional edifice of inderite is therefore built by heteropolyhedral Mg(H2O)4B3O3(OH)5 clusters mutually connected by H-bonds, mediated by the zeolitic (“interstitial”) H2O molecules lying between the clusters, so that the correct form of the chemical formula of inderite is Mg[B3O3(OH)5](H2O)4·H2O, rather than MgB3O3(OH)5·5H2O. All the thirteen independent oxygen sites of the structure are involved in H-bonding, as donors or as acceptors. This confirms the pervasive nature and the important role played by the H-bonding network on the structural stability of inderite. The differences between the crystal structure of the two dimorphs inderite and kurnakovite are discussed.

通过波长色散模式下的电子探针显微分析、激光烧蚀-(多收集器-)电感耦合等离子体-质谱法和单晶中子衍射法,对克拉玛依矿床中已知理想分子式为 MgB3O3(OH)5-5H2O 的水合硼酸盐英得莱石的晶体化学进行了重新研究。化学数据证明,所研究的橄榄石的实际成分与理想成分基本相同,潜在的同构取代基含量极少,因此,除 B 外,橄榄石不含任何其他工业相关元素(例如,锂浓度低于 2.5 wt ppm,Be 或 REE 低于 0.1 wt ppm)。δ11BNIST951 的平均值约为 7 ‰。- 平均δ11BNIST951值约为7‰,属于硼源可归因于陆地储层(如热液卤水)而非海洋储层的数值范围。在 280 开氏度和 10 开氏度下进行的中子结构细化证实,橄榄石结构的组成单元包括:两个 BO2(OH)2 四面体(sp3 电子构型的硼离子)和一个 BO2(OH) 三角形(sp2 电子构型的硼离子),它们通过角共享连接成一个(山梨硼酸盐)B3O3(OH)5 环,以及一个镁八面体 Mg(OH)2(OH2)4。B3O3(OH)5环和八面体镁通过分角连接,形成一个孤立的Mg(H2O)4B3O3(OH)5(分子)簇。因此,橄榄石的三维结构是由异多面体 Mg(H2O)4B3O3(OH)5簇通过 H 键相互连接而成的,并由位于簇之间的沸石("间隙")H2O 分子介导,因此橄榄石的正确化学式是 Mg[B3O3(OH)5](H2O)4-H2O,而不是 MgB3O3(OH)5-5H2O。该结构中所有 13 个独立的氧位点都参与了氢键作用,无论是作为供体还是作为受体。这证实了 H 键网络对橄榄石结构稳定性的普遍性和重要作用。本文还讨论了英达石和库尔纳克维石这两种非晶态晶体结构之间的差异。
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Physics and Chemistry of Minerals
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