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Characterization and comparison of natural and Zachery-treated turquoise: new data 天然绿松石和zachery处理绿松石的特性和比较:新数据
IF 1.4 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2023-06-16 DOI: 10.1007/s00269-023-01241-w
Valeria Diella, Marco Cantaluppi, Rosangela Bocchio, Elena Possenti, Ilaria Adamo, Giancarlo Della Ventura, Lucia Mancini, Nicoletta Marinoni

Turquoise is a well-known gemstone that has been used in artefacts across many cultures throughout history. However, due to its porosity it is often treated to enhance its color and beauty. One appreciated treatment is the patented Zachery process, although its details remain publicly undisclosed. Previous studies indicated that only a high K content distinguishes Zachery-treated from natural turquoises. In this study, natural and Zachery-treated turquoise samples from the famous Kingman mine, Arizona, USA, were analysed by means a multi-methodological approach, including standard gemological testing, electron microprobe (EMPA), scanning electron microscope with energy dispersive spectrometer (SEM–EDS) and X-ray diffraction (XRD), Fourier-Transform InfraRed (FTIR), non-destructive External Reflection-Fourier-Transform InfraRed (ER-FTIR) spectroscopy and X-ray computed microtomography (μCT). The results revealed new chemical–mineralogical and microstructural features that distinguish the Zackery-treated from the natural turquoise: higher specific gravity and lower porosity, associated with high and uneven concentrations of Cu, K and Na, the occurrence of tenorite (CuO), the presence and extension of reaction edges in the entire volume are distinctive of treated samples. Moreover, Cu-rich seeds and feldspar crystals may be interpreted as additional components used during the treatment. The hypothesis is that the Zachery treatment induces the re-crystallization of a new turquoise-like phase, which differs from the natural one from a chemical and microstructural point of view.

绿松石是一种众所周知的宝石,在历史上许多文化中都被用于人工制品。然而,由于其多孔性,它经常被处理以增强其颜色和美观。一种受欢迎的治疗方法是获得专利的Zachery方法,尽管其细节尚未公开。先前的研究表明,只有高钾含量才能将扎克里处理的绿松石与天然绿松石区分开来。采用标准宝石学检测、电子探针(EMPA)、扫描电子能谱仪(SEM-EDS)和x射线衍射仪(XRD)、傅里叶变换红外(FTIR)、无损外反射-傅里叶变换红外(ER-FTIR)光谱和x射线计算机显微断层扫描(μCT)等多种方法对美国亚利桑那州著名的金曼矿的天然绿松石和经zachry处理的绿松石样品进行了分析。研究结果揭示了与天然绿松石不同的化学矿物学和微观结构特征:较高的比重和较低的孔隙度,Cu、K和Na浓度高且不均匀,铜钼矿(CuO)的存在,反应边缘的存在和延伸是处理样品的特征。此外,富铜种子和长石晶体可能被解释为处理过程中使用的附加成分。假设是,Zachery处理诱导了一种新的绿松石样相的再结晶,从化学和微观结构的角度来看,这种相与自然相不同。
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引用次数: 0
Lattice thermal conductivity of Mg2SiO4 olivine and its polymorphs under extreme conditions 极端条件下Mg2SiO4橄榄石及其多晶的晶格热导率
IF 1.4 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2023-04-29 DOI: 10.1007/s00269-023-01240-x
Shu Yang, Wenxin Dong, Li Zhang, Kaihua He, Wei Dai, Chen Lu

The thermal transport properties of minerals at high temperature and high pressure are important for understanding the internal evolution and dynamic processes of the Earth. Here, we carry out a detailed study on the lattice thermal conductivities (({kappa }_text {latt})) of (text {Mg}_2text {SiO}_4) under upper mantle and transition zone conditions by anharmonic lattice dynamics method. The calculations show that the ({kappa }_text {latt}) of (text {Mg}_2text {SiO}_4) increase with the phase transitions, which agree with the previous measurements and are attributed to the increase of lifetime and group velocity under extreme conditions. The ({kappa }_text {latt}) of (text {Mg}_2text {SiO}_4) along the geotherm shows a 64(%) jump at 410 ({textrm{km}}) and 71(%) jump at 520 (textrm{km}). The anisotropy in the ({kappa }_text {latt}) of olivine and wadsleyite decreases with increasing pressure. The present findings offer a fundamental knowledge of the ({kappa }_text {latt}) of (text {Mg}_2text {SiO}_4) under extreme conditions, which are crucially important for understanding the thermal transport processes in the Earth.

矿物在高温高压下的热输运性质对认识地球内部演化和动力学过程具有重要意义。本文采用非调和晶格动力学方法对上地幔和过渡带条件下(text {Mg}_2text {SiO}_4)的晶格热导率(({kappa }_text {latt}))进行了详细的研究。计算表明,(text {Mg}_2text {SiO}_4)的({kappa }_text {latt})值随着相变的增大而增大,这与之前的测量结果一致,这是由于极端条件下寿命和群速度的增大。沿地热方向的(text {Mg}_2text {SiO}_4)的({kappa }_text {latt})在410 ({textrm{km}})处跳跃64 (%),在520 (textrm{km})处跳跃71 (%)。随着压力的增加,橄榄石和瓦德斯莱石的({kappa }_text {latt})各向异性减小。目前的发现提供了极端条件下(text {Mg}_2text {SiO}_4)的({kappa }_text {latt})的基本知识,这对于理解地球的热传输过程至关重要。
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引用次数: 0
Lanthanide and yttrium substitution in natural fluorite 天然萤石中的镧系元素和钇取代
IF 1.4 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2023-04-27 DOI: 10.1007/s00269-023-01239-4
Nicola J. Horsburgh, Adrian A. Finch, Henrik Friis

Fluorite is one of the most common minerals in the crust and is of widespread economic importance. It shows strong UV-excited luminescence, variously attributed to defects within the fluorite structure and lanthanide substitutions. We present here a detailed chemical characterisation of a suite of natural fluorite samples, chosen to represent the range of compositions observed in nature. We perform X-ray excited luminescence spectroscopy on the samples as a function of temperature (20–673 K) in the wavelength range 250–800 nm to provide insights into physical defects in the lattice and their interactions with lanthanide substituents in natural fluorite. Most broad bands in the UV are attributed to electronic defects in the fluorite lattice, whereas sharp emissions are attributed to intra-ion energy cascades in trivalent lanthanides. Lanthanides are accommodated in fluorite by substitution for Ca2+ coupled with interstitial F, O2− (substituting for F) and a variety of electronic defect structures which provide local charge balance. The chondrite-normalised lanthanide profiles show that fluorite accommodates a greater proportion of heavy lanthanides (and Y) as the total Rare Earth Element (REE) concentration increases; whereas cell parameters decrease and then increase as substitution continues. Luminescence intensity also goes through a maximum and then decreases as a function of REE concentration. All three datasets are consistent with a model whereby lanthanides initially act as isolated centres, but, beyond a critical threshold (~ 1000 ppm), cluster into lanthanide-rich domains. Clustering results in shorter REE-O bond distances (favouring smaller heavier ions), a larger unit cell but more efficient energy transfer between lanthanides, thereby promoting non-radiative energy loss and a drop in the intensity of lanthanide emission.

萤石是地壳中最常见的矿物之一,具有广泛的经济意义。它表现出强烈的紫外光激发发光,不同的原因是萤石结构的缺陷和镧系元素的取代。我们在这里介绍了一套天然萤石样品的详细化学特征,选择代表自然界中观察到的成分范围。我们对250-800 nm波长范围内温度(20-673 K)的样品进行x射线激发发光光谱分析,以深入了解晶格中的物理缺陷及其与天然萤石中镧系取代基的相互作用。紫外线中的大多数宽频带归因于萤石晶格中的电子缺陷,而尖锐的发射归因于三价镧系元素中的离子内能量级联。萤石中的镧系元素是通过取代Ca2+和间隙的F−、O2−(取代F−)以及提供局部电荷平衡的各种电子缺陷结构来容纳的。球粒正态镧系元素剖面显示,随着稀土元素(REE)总浓度的增加,萤石中重镧系元素(和Y)的比例增大;而细胞参数则随着置换的进行先减小后增大。发光强度随稀土浓度的变化也先达到最大值,然后逐渐减小。所有三个数据集都与一个模型相一致,即镧系元素最初作为孤立的中心,但超过临界阈值(~ 1000ppm),聚集成富镧系元素域。聚类导致更短的REE-O键距离(有利于较小的重离子),更大的单元电池,但更有效的镧系元素之间的能量转移,从而促进非辐射能量损失和镧系元素发射强度的下降。
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引用次数: 1
Thermal expansivity and high-pressure sound velocities of natural topaz and implications for seismic velocities and H2O and fluorine recycling in subduction zones 天然黄玉的热膨胀率和高压声速及其对俯冲带地震速度和水和氟再循环的影响
IF 1.4 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2023-04-17 DOI: 10.1007/s00269-023-01238-5
Mingsheng Zhao, Nao Cai, Duojun Wang, Qiong Liu

Topaz is an important mineral formed in deeply subducted sediments and might be a major carrier of both H2O and fluorine into the Earth’s interior. To better understand the seismic velocities and H2O and fluorine recycling in subduction zones, we determined the thermal expansivity of a natural topaz (Al1.93(1)Si1.06(1)O4(OH)0.48(3)F1.52(3), space group pbnm) up to 1073 K using high-temperature powder X-ray diffraction. No phase transition or decomposition was observed within the investigated temperature range. The volume thermal expansion coefficient is 2.24(1) × 10–5 K−1, and the ratio of the axial thermal expansion coefficients α0(a):α0(b):α0(c) is 1.15:1:1.32 at 300 K. We also investigated its compressional (P) and shear (S) wave velocities up to 13.6 GPa at room temperature using ultrasonic interferometry in a multi-anvil apparatus. The adiabatic bulk modulus (Ks) and shear modulus (G) of topaz and their pressure derivatives are KS0 = 151(1) GPa, KS = 4.9(1), G0 = 109.4(10) GPa, and G′ = 1.8(1), respectively, by fitting the velocities and density data to finite strain equations. The density and velocity profiles of the topaz were calculated under the upper mantle P–T conditions. Our results reveal that topaz is prone to subduction which drives H2O and fluorine to migrate to the deep Earth. Meanwhile, topaz also has unusually high VP and VS, and low VP/VS ratio relative to common upper mantle phases and the preliminary reference Earth model (PREM, Dziewonski and Anderson, Phys Earth Planet Inter 25:297–356, 1981), which may be diagnostic seismic properties in subducted slabs.

黄玉是一种重要的矿物,形成于深俯冲的沉积物中,可能是水和氟进入地球内部的主要载体。为了更好地了解俯冲带的地震速度和水和氟的再循环,我们利用高温粉末x射线衍射测定了天然黄玉(Al1.93(1)Si1.06(1)O4(OH)0.48(3)F1.52(3),空间群pnm)高达1073 K的热膨胀率。在所研究的温度范围内未观察到相变或分解。在300 K时,体积热膨胀系数为2.24(1)× 10-5 K−1,轴向热膨胀系数α0(a):α0(b):α0(c)之比为1.15:1:1.32。我们还利用超声干涉测量技术在室温下测量了其高达13.6 GPa的纵波(P)和横波(S)波速。通过将速度和密度数据拟合到有限应变方程中,得到黄玉的绝热体模量(Ks)和剪切模量(G)及其压力导数分别为KS0 = 151(1) GPa、Ks′= 4.9(1)、G0 = 109.4(10) GPa和G′= 1.8(1)。在上地幔P-T条件下,计算了黄玉的密度和速度分布。我们的研究结果表明,黄玉容易发生俯冲,这促使水和氟向地球深部迁移。与此同时,相对于普通上地幔相和初步参考地球模型(PREM, Dziewonski和Anderson, Phys Earth Planet Inter 25:297-356, 1981),黄玉具有异常高的VP和VS,且VP/VS比较低,这可能是俯冲板块地震特性的诊断。
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引用次数: 0
Compressional behavior of the aragonite-structure carbonates to 6 GPa 文石结构碳酸盐在6gpa下的压缩行为
IF 1.4 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2023-04-05 DOI: 10.1007/s00269-023-01237-6
Isaac Vidal-Daza, Antonio Sánchez-Navas, Alfonso Hernández-Laguna

The behaviors of aragonite (CaCO(_3)), strontianite (SrCO(_3)), cerussite (PbCO(_3)), and witherite (BaCO(_3)) at increasing pressure have been studied up to 6 GPa using density functional theory with plane waves. A parallelism of the orthorhombic carbonates with the closed-packed AsNi structure is considered in our analysis, being the CO(_3^{2-}) groups not centered in the interstice of the octahedron. The decomposition of the unit-cell volume into atomic contributions using the Quantum Theory of Atoms in Molecules has allowed the analysis of the bulk modulus in atomic contributions. The bulk, axes, interatomic distances, and atomic compressibilities are calculated. The largest compression is on the c crystallographic axis, and the c linear modulus has a linear function with the mineral bulk modulus ((K_0)). Many of the interatomic distances moduli of the alkaline earth (AE) carbonates show linear functions with the bulk modulus; however, the whole series (including cerussite) only gives linear functions when (K_0) is related either with the CC distances modulus or the modulus of the distances of the C to the faces of the octahedron perpendicular to c. These last distances are the projections of the Metal–Oxygen (MO) distances to the center of the octahedron. (K_{0AE}) carbonates also show linear functions with the atomic moduli of their cations. However, the whole series show a linear relation with the atomic modulus of C atoms. Therefore, the whole series highlight the importance of the C atoms and their interactions in the mechanism of compression of the orthorhombic carbonate series.

利用平面波密度泛函理论研究了文石(CaCO (_3))、锶矿(SrCO (_3))、铜矿(PbCO (_3))和辉石(BaCO (_3))在6 GPa压力下的行为。在我们的分析中考虑了正交碳酸盐与封闭堆积的AsNi结构的平行性,即CO (_3^{2-})基团不在八面体的间隙中。利用分子中原子的量子理论将单元胞体积分解为原子贡献,可以分析原子贡献中的体积模量。计算了体积、轴、原子间距离和原子可压缩性。最大压缩发生在c晶轴上,c线性模量与矿物体积模量成线性函数关系((K_0))。碱土碳酸盐的许多原子间距离模量与体积模量呈线性关系;然而,当(K_0)与碳原子距离模量或碳原子与垂直于碳原子的八面体的面之间的距离模量有关时,整个系列(包括铈)只给出线性函数。这些最后的距离是金属-氧(MO)到八面体中心的距离的投影。(K_{0AE})碳酸盐也表现出与其阳离子的原子模量的线性函数。但整个级数与C原子的原子模量呈线性关系。因此,整个系列突出了C原子及其相互作用在正方晶碳酸盐系列压缩机制中的重要性。
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引用次数: 0
An experimental study of proton implantation in olivine 质子注入橄榄石的实验研究
IF 1.4 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2023-04-05 DOI: 10.1007/s00269-023-01234-9
Thilo Bissbort, Qinting Jiang, Hans-Werner Becker, Varvara Foteinou, Sumit Chakraborty

Implantation of ions in minerals by high energy radiation is an important process in planetary and materials sciences. For example, the solar wind is a multi-ion flux that progressively modifies the composition and structure of near-surface domains in solar objects, like asteroids. A bombardment of a target by different elements like hydrogen (H) at various energies causes, among other things, the implantation of these particles in crystalline and amorphous materials. It is important to understand the mechanisms and features of this process (e.g., how much is implanted and retained), to constrain its contribution to the chemical budget of solar objects or for planning various material-science applications. Yet, there has been no detailed study on H implantation into olivine (e.g., the quantification of maximum retainable H), a major mineral in this context. We performed experiments on H implantation in San Carlos olivine at 10 and 20 keV with increasing fluences (up to 3×1018 at/cm2). Nanoscale H profiles that result from implantation were analyzed using Nuclear Resonance Reaction Analysis after each implantation to observe the evolution of the H distribution as a function of fluence. We observed that after a systematic growth of the characteristic, approximately Gaussian shaped, H profiles with increasing fluences, a maximum concentration at H ~ 20 at% is attained. The maximum concentration is approximately independent of ion energy, but the maximum penetration depth is a function of beam energy and is greater at higher energies. The shapes of the profiles as well as the maximum concentrations deviate from those predicted by currently available models and point to the need for direct experimental measurements. We compared the depth profiles with predictions by SRIM. Based on observations from this study, we were able to constrain the maximum retainable H in olivine as a function of ion energy.

高能辐射在矿物中注入离子是行星科学和材料科学中的一个重要研究过程。例如,太阳风是一种多离子流,它逐渐改变太阳物体(如小行星)近表面区域的组成和结构。不同的元素,如氢(H)以不同的能量轰击目标,会导致这些粒子在晶体和非晶态材料中植入。了解这一过程的机制和特征(例如,植入和保留了多少),限制其对太阳能物体化学预算的贡献或规划各种材料科学应用是很重要的。然而,目前还没有关于氢注入橄榄石的详细研究(例如,最大可获得氢的量化),橄榄石是这方面的主要矿物。我们在圣卡洛斯橄榄石中进行了10和20 keV的H注入实验,影响越来越大(高达3×1018 at/cm2)。每次注入后,利用核共振反应分析对注入后的纳米尺度H谱进行分析,观察H分布随通量的变化。我们观察到,随着影响的增加,特征近似高斯形的H曲线系统增长后,在H ~ 20 %处达到最大浓度。最大浓度与离子能量无关,但最大穿透深度与束流能量有关,且能量越高,最大穿透深度越大。剖面的形状以及最大浓度偏离了目前可用的模型所预测的结果,表明需要进行直接的实验测量。我们将深度剖面与SRIM预测进行了比较。根据本研究的观察,我们能够约束橄榄石中最大可保留H作为离子能量的函数。
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引用次数: 2
Thermal expansion of anhydrous copper sulfate minerals determined by single crystal X-ray diffraction: chalcocyanite CuSO4, dolerophanite Cu2OSO4 and kamchatkite KCu3O(SO4)2Cl 用单晶x射线衍射测定无水硫酸铜矿物:黄铜矿cuo4、白云石Cu2OSO4和堪察凯特kcu30 (SO4)2Cl的热膨胀
IF 1.4 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2023-04-04 DOI: 10.1007/s00269-023-01236-7
Evgeny V. Nazarchuk, Oleg I. Siidra, Stanislav K. Filatov, Dmitri O. Charkin, Lada R. Zhdanova

Polythermic single-crystal X-ray studies of chalcocyanite CuSO4, dolerophanite Cu2OSO4, and kamchatkite KCu3O(SO4)2Cl have established their melting points as well as peculiarities of their thermal expansion. Association of oxocentered and sulfate tetrahedra in dolerophanite and kamchatkite leads to the formation of rigid tetrahedral “backbones” only slightly sensitive to thermal variations. Rigid complexes can also be distinguished in the structure of chalcocyanite, if we consider only the system of the shortest and strongest Cu–O and S–O bonds. The anisotropy of the thermal expansion can be explained by either rigid complexes drifting parallel to each other (as in dolerophanite and chalcocyanite), or radial and angular distortions in the polyhedra of alkali cations. The presence of a tetrahedrally coordinated additional oxygen atom in the structure of dolerophanite and kamchatkite leads to an increase in the principal eigenvalues. The demonstrated rigidity of the sulfate tetrahedra in studied anhydrous copper sulfate minerals explains the absence of phase transitions up to the melting temperatures. The variation of chemical composition leads to changes in their thermal decomposition points. Chlorine-containing kamchatkite decomposes at the lowest temperature of 590(5) K, next are chalcocyanite 675(10) K, and dolerophanite 925(10) K.

对黄铜矿CuSO4、白云石Cu2OSO4和堪察凯特kcu30 (SO4)2Cl的多热单晶x射线研究确定了它们的熔点和热膨胀特性。在白云石和堪察石中,氧中心和硫酸盐四面体的结合导致刚性四面体“骨架”的形成,对热变化仅轻微敏感。如果我们只考虑最短和最强的Cu-O和S-O键的系统,那么在黄铜矿的结构中也可以区分出刚性配合物。热膨胀的各向异性可以用相互平行漂移的刚性配合物(如在白云石和黄铜矿中)或碱阳离子多面体的径向和角度扭曲来解释。白云石和堪察石结构中四面体配位附加氧原子的存在导致了主特征值的增加。所研究的无水硫酸铜矿物中硫酸盐四面体的刚性解释了在熔融温度之前没有相变的原因。化学成分的变化导致其热分解点的变化。含氯堪察石的最低分解温度为590(5)K,其次是黄铜矿675(10)K,白云石925(10)K。
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引用次数: 0
Nanomechanics of minerals: understandings and developments through instrumented nanoindentation techniques 矿物的纳米力学:通过仪器纳米压痕技术的理解和发展
IF 1.4 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2023-02-28 DOI: 10.1007/s00269-023-01235-8
Rajiv Mukherjee, Santanu Misra

Understanding the dynamics of the lithosphere relies heavily on the scale-dependent rheology of minerals. While quartz, feldspar, and phyllosilicates are the key phases to govern the rheology of the crust and tectonic margins, olivine and other mafic phases control the same in the upper mantle. Phase transition, solid-state substitution, polymorphism, etc. also affect mineral phase rheology. High pressure–temperature deformation tests with natural, synthetic and analog materials have improved our interpretation of the geodynamic state of the lithosphere. However, deforming and studying a single crystal is not easy, because of the scarcity of specimens and laborious sample preparations. Experimental micro- to nanoindentation at room and/or elevated temperatures has proven to be a convenient method over mesoscale compressive testing. Micro- to nanoindentation technique enables higher precision, faster data acquisition and ultra-high resolution (nanoscale) load and displacement. Hardness, elastic moduli, yield stress, fracture toughness, fracture surface energy and rate-dependent creep of mono- or polycrystalline minerals are evaluated using this technique. Here, we present a comprehensive assessment of micro- to nano-mechanics of minerals. We first cover the fundamental theories of instrumented indentation, experimental procedures, pre- and post-indentation interpretations using various existing models followed by a detailed discussion on the application of nanoindentation in understanding the rheology and deformation mechanisms of various minerals commonly occur in the crust and upper mantle. We also address some of the major limitations of indentation tests (e.g., indentation size effect). Finally, we suggest potential future research areas in mineral rheology using instrumented indentation.

了解岩石圈的动力学在很大程度上依赖于矿物的尺度流变性。石英、长石和层状硅酸盐是控制地壳和构造边缘流变的关键相,而橄榄石和其他基性相在上地幔中也起着同样的作用。相变、固态取代、多态等也会影响矿物的相流变。用天然材料、合成材料和模拟材料进行的高压-高温变形试验改进了我们对岩石圈地球动力学状态的解释。然而,变形和研究单晶并不容易,因为样品稀缺和样品制备工作费力。在室温和/或高温下的实验微纳米压痕已被证明是一种比中尺度压缩测试更方便的方法。微到纳米压痕技术可以实现更高的精度,更快的数据采集和超高分辨率(纳米级)负载和位移。硬度,弹性模量,屈服应力,断裂韧性,断裂表面能和速率依赖蠕变的单晶或多晶矿物使用该技术进行评估。在这里,我们提出了一个综合评估的微观到纳米力学的矿物。我们首先介绍了仪器压痕的基本理论、实验过程、利用各种现有模型对压痕前后的解释,然后详细讨论了纳米压痕在理解地壳和上地幔中常见的各种矿物的流变和变形机制中的应用。我们还讨论了压痕测试的一些主要限制(例如,压痕尺寸效应)。最后,我们提出了利用仪器压痕研究矿物流变学的潜在未来研究领域。
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引用次数: 0
Mineralogical characterization of fluorescent grossular garnet var. tsavorite from Merelani Hills, Tanzania 坦桑尼亚Merelani山萤光粗红石榴石变种沙长石的矿物学特征
IF 1.4 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2023-02-16 DOI: 10.1007/s00269-023-01233-w
Alfredo Idini, Celestino Angeli, Franco Frau, Guido Ennas, Stefano Naitza, Giovanni Battista De Giudici, Roberto Argazzi

Tsavorite is the trade name for the green vanadium–chromium variety of grossular occurring in the Precambrian terrains in the areas of Merelani Hills (Tanzania) and Tsavo Park (Kenya) which are by far the most important source of gem grade specimens of tsavorite used for high jewellery. The tsavorite crystals from Merelani Hills exhibit a pink-red and yellow fluorescence when irradiated by common portable UV lamp, an unusual phenomenon among members of the garnet group. The electron density map calculated from the diffraction data and plotted against a grossular standard shows that an excess of negative charge is clearly pinpointed in the crystallographic site occupied by Al3+. The bulk elemental analysis shows that the most represented end-member, besides grossular, is the vanadium-bearing goldmanite garnet (3.82–4.08 mol %). The fluorometry with an excitation beam at 408 nm indicates a complex emission pattern with the most intense emissions at 701 and 716 nm and subordinately at 592 nm. The colour perception is dominated by the emission yellow band at 592 nm while the contribution of the red band modulates the colour ranging from bright orange to pink-red. The attribution of the emission at 592 nm is related to Mn2+ while the emissions at 701 and 716 nm could be related to the chromium content and/or to a possible fraction of vanadium as V2+. Because of the characteristic colour perceived under UV light, the use of a common led lamp can be useful as a diagnostic tool to easily identify tsavorite.

Tsavorite是一种绿色的钒铬金属榴石的商品名称,产于Merelani Hills(坦桑尼亚)和Tsavo Park(肯尼亚)地区的前寒武纪地形,是迄今为止用于高级珠宝的Tsavorite宝石级标本的最重要来源。在普通便携式紫外灯照射下,来自Merelani山的沙弗石晶体呈现出粉红色、红色和黄色的荧光,这在石榴石群成员中是一种不寻常的现象。根据衍射数据计算出的电子密度图,并根据总体标准绘制,表明在Al3+占据的晶体位置上明显存在过量的负电荷。体元素分析表明,除粗晶外,最具代表性的端元是含钒金榴石石榴石(3.82 ~ 4.08 mol %)。408 nm激发光束的荧光测量显示出复杂的发射模式,在701和716 nm处发射最强烈,其次是在592 nm处。在592 nm处的黄色波段占主导地位,而红色波段的贡献调节了从亮橙色到粉红色的颜色范围。592 nm处的发射归因与Mn2+有关,而701和716 nm处的发射可能与铬含量和/或钒作为V2+的可能部分有关。由于在紫外光下感知到的特征颜色,使用普通的led灯可以作为一种有用的诊断工具来轻松识别沙沃莱特。
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引用次数: 0
Mechanisms and conditions of Ti and Cr incorporation in mantle phlogopite: the results of atomistic simulation 地幔辉云母中Ti和Cr掺入的机制和条件:原子模拟的结果
IF 1.4 4区 地球科学 Q4 MATERIALS SCIENCE, MULTIDISCIPLINARY Pub Date : 2023-02-10 DOI: 10.1007/s00269-023-01232-x
Aleksandra A. Bendeliani, Nikolay N. Eremin, Andrey V. Bobrov

Modeling of eight mechanisms for the incorporation of Ti4+ and Cr3+ impurity components into phlogopite was carried out by a semi-empirical method using the GULP (General Utility Lattice Program) software. The calculation of thermodynamic mixing properties in the range of 1–7 GPa and 373–1573 K and the analysis of the structure geometry for the simulated solid solutions provided the following energy-preferred schemes of isomorphic substitution: VI(Mg2+) + 2IV(Si4+) = VI(Ti4+) + 2IV(Al3+) and VI(Mg2+) + 2IV(Al3+) = VI(□) + 2IV(Ti4+), VI(Mg2+) + IV(Si4+) = VI(Cr3+) + IV(Al3+), and 3VI(Mg2+) = VI(Al3+) + VI(Cr3+) + VI(□). It is shown the scheme 2VI(Mg2+) = VI(Ti4+) + VI(□) illustrating entrance of Ti with the formation of a vacancy is realized in the case of microconcentrations of Ti only. Accumulation of high-Ti contents associates with the formation of a vacancy in the octahedral site. This provides incorporation of Ti via the schemes VI(Mg2+) + 2IV(Al3+) = VI(□) + 2IV(Ti4+) and (Mg, Fe2+) + 2OH = Ti4+  + 2O2− only. It is shown that incorporation of high-Cr concentrations (> 5.5 wt % Cr2O3) is accompanied by an increase in the number of vacancies in the octahedral site with an increase in the proportion of the dioctahedral component K(Al, Cr, □)2AlSi3O10(OH)2.

利用GULP (General Utility Lattice Program)软件,采用半经验方法对8种Ti4+和Cr3+杂质组分掺入云母的机理进行了建模。通过1 - 7gpa和373-1573 K范围内的热力学混合性质计算和模拟固溶体的几何结构分析,得出了以下能量优先的同构取代方案:VI(Mg2+) + 2IV(Si4+) = VI(Ti4+) + 2IV(Al3+)和VI(Mg2+) + 2IV(Al3+) = VI(□)+ 2IV(Ti4+)、VI(Mg2+) + IV(Si4+) = VI(Cr3+) + IV(Al3+)和3VI(Mg2+) = VI(Al3+) + VI(Cr3+) + VI(□)。结果表明,2VI(Mg2+) = VI(Ti4+) + VI(□)表明,只有在微量浓度的情况下,才实现了Ti的入口与空位的形成。高钛含量的积累与八面体空位的形成有关。这提供了Ti通过方案VI(Mg2+) + 2IV(Al3+) = VI(□)+ 2IV(Ti4+)和(Mg, Fe2+) + 2OH−= Ti4+ + 2O2−。结果表明,高Cr浓度(> 5.5 wt % Cr2O3)的掺入伴随着八面体空位数量的增加和二面体成分K(Al, Cr,□)2AlSi3O10(OH)2比例的增加。
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Physics and Chemistry of Minerals
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