Mineralogy and Petrology最新文献

Hopmannite, ideally Ba₂(Ti₅Fe)O₁₃, is a new Ba-dominant hexatitanate discovered in xenoliths enclosed within the basaltic host rocks of the Bellerberg volcano in Germany. The mineral exhibits black to dark-grey thin platy crystals, with submetallic lustre and a perfect cleavage along (100). The empirical formula of the holotype hopmannite, calculated on the basis of 8 cations and 13 O atoms, is (Ba_1.00K_0.61Na_0.24Sr_0.08Ca_0.04)_Σ1.97(Ti_5.36 Fe²⁺_0.48Fe³⁺_0.13Mg_0.06)_Σ6.03O₁₃. Hopmannite is monoclinic, space group C2/m, with a = 15.357(2) Å, b = 3.8500(7) Å, c = 9.129(2) Å, β = 99.033(10)°, V = 533.03(17) ų and Z = 2 and is isostructural with nixonite, Na₂Ti₆O₁₃ and jeppeite, K₂Ti₆O₁₃. The structure of hopmannite consists of a fundamental unit composed of three edge-shared Ti-octahedra duplicated above and below in the direction of the b-axis, which form an open octahedral framework enclosing a tunnel, cubic-like sites occupied by Ba, K, and Na. The structural results are consistent with the chemical data and show that the Ba²⁺ content is greater than K⁺ and Na⁺ at the A-cation site. Spectroscopic analyses indicated that the presence of the main vibrations is related to TiO₆ octahedra, including Ti-O and Ti-O-Ti stretching vibrations. Hopmannite, along with fresnoite and batisite, represents a mineral assemblage formed late in the crystallisation sequence at temperatures below 1000 °C from a highly alkaline residual melt enriched in incompatible elements such as Ba, Sr, Ti, Zr, and P.

The distinction between magmatic and solid-state flow can be complex in some rocks, especially rhyolites, which tend to deform differently than other quartz-feldspathic rocks. Furthermore, this type of study in Paleoarchean rhyolites is extremely rare. In this sense, this work presents field data, microstructural analysis, and electron-backscatter diffraction (EBSD) analyses of quartz porphyroclasts and aggregates from the 3.3 Ga Contendas Rhyolite in the Gavião Block, northeastern Brazil. The Contendas Rhyolite presents the superposition of magmatic and solid-state processes. It displays preserved igneous characteristics (such as euhedral feldspar phenocrysts, feldspars with rapakivi microstructure, and quartz porphyroclasts with primary embayments) coexisting with solid-state deformation microstructures (recrystallized tails, recrystallized elongated aggregates of quartz, and deformation twins). There is evidence that the magmatic flow occurred in the N-S direction, defined by the N-S alignment of feldspar phenocrysts and quartz porphyroclasts, and by the N-S orientation of the [c] axes of the parent grains of the quartz porphyroclasts. On the other hand, quartz porphyroclasts were deformed by dislocation creep, with dominance of the prism (leftlangle arightrangle) slip, and recrystallize by subgrain-rotation. The approximately N-S trending tectonic foliation and up-dip mineral stretching lineation of the Contendas Rhyolite indicate that solid-state deformation occurred in the E-W direction, which favored the preservation of the magmatic fabric. Moreover, the microstructural and textural characteristics of the Contendas Rhyolite define medium-grade solid-state deformation, with a temporal break between magmatic and solid-state flows.

Southeast China hosts extensive Late Mesozoic metallogenic systems, including metallic and non-metallic deposits genetically linked to tectonic-thermal events. Central Zhejiang Province, a major fluorite-producing region in China, exhibits spatiotemporal relationships with the Cretaceous magmatic-hydrothermal activity. In this study, zircon U–Pb and fluorite Sm–Nd geochronology, whole-rock/mineral geochemistry, Sr–Nd–H–O–Ca isotopes, and fluid inclusion microthermometry were used to constrain the genesis of the Shanwang fluorite deposit in the Mazhai caldera, central Zhejiang. Fluorite orebodies are structurally controlled by intracaldera faults and contain fluorite–quartz–barite–pyrite–pyrophyllite assemblages. Geochronological data revealed that fluorite mineralization (77 Ma, Sm–Nd isochron age) postdated the Early Cretaceous caldera-forming volcanism (128–125 Ma, zircon U–Pb age). Fluid inclusion data indicated low-temperature (128–184 °C) and low-salinity (0.2–8.8 wt.% NaCl eqv.) hydrothermal conditions. Stable isotopes (δD_VSMOW = -101.8‰ to -64.9‰, δ¹⁸O_VSMOW = -10.4‰ to -6.9‰) confirm meteoric water-dominated fluids. Integrated Sr–Nd–Ca isotopes (fluorite δ^44/40Ca values = 1.29–1.35‰) and trace element characteristics demonstrate that ore-forming materials were primarily leached from volcanic rocks via meteoric water–rock interaction in a paleo-geothermal system, with subsequent migration along fault zones leading to fluorite precipitation. Mineralization is correlated with Late Cretaceous lithospheric extension driven by the Paleo-Pacific slab rollback beneath Southeast China.

In this second article dedicated to the structural analysis of twins in feldspars, we present the results for albite and pericline twins in alkali triclinic feldspars. The strong monoclinic structural pseudo-symmetry and orthorhombic metric pseudo-symmetry of the lattice are considered the rationale for the occurrence of both albite and pericline as growth twins. However, these pseudo-symmetries are less marked for triclinic albite than for microcline. This results in a stronger distortion of the coordination polyhedra at the composition plane for pericline twins, whose occurrence should therefore be less probable than in microcline. The old hypothesis that pericline twinning should be only possible as growth twin when the rhombic section approaches the (001) pinacoid, i.e. in plagioclases, seems contradicted by the computed atomic structure at the composition plane. The structure is less distorted in the case of microcline, i.e. when the rhombic section approaches the (200) pinacoid, making pericline twinning more probable as growth twin in microcline.

Continental intraplate basalts exhibit diverse geochemical characteristics that reflect complex mantle processes beneath East Asia. In eastern China, the tectonic evolution of the North China Craton has been linked to lithospheric thinning, asthenospheric upwelling, and metasomatic modification associated with Pacific slab subduction. However, the petrogenetic mechanisms and mantle source characteristics of the Cenozoic basalts in Anhui Province remain inadequately constrained. Here we show that the geochemical and isotopic compositions of basalts from Anhui Province indicate a heterogeneous mantle source modified by carbonatitic metasomatism. Major and trace element analyses, REE patterns, and Sr-Nd isotopic data reveal three primary magma types—alkali basalts, tholeiitic basalts, and Nushan alkali basalts—formed through varying degrees of partial melting (1–5 vol%, 15 vol%, and 1–10 vol%, respectively) followed by fractional crystallization. Trace element ratios (e.g., Zr/Sm–Hf/Sm, La/Nb–⁸⁷Sr/⁸⁶Sr) suggest that the mantle beneath Anhui underwent enrichment by carbonated eclogite-derived melts related to subducted Pacific slab materials. The isotopic compositions indicate a mixing of depleted MORB mantle (DMM) and enriched mantle type-1 (EM-1) sources, with younger basalts showing more depleted signatures. These findings provide new insights into the long-term geochemical evolution of the subcontinental lithospheric mantle beneath eastern China and highlight the importance of multi-stage metasomatism and subduction-derived enrichment in shaping the region’s intraplate magmatism.

In this work, we describe a new genetic occurrence of wakefieldite-(Ce) in association with monazite-(Ce) and rhabdophane-(Ce) from K-feldspar clusters in hydrothermal hematite veins of the Mys Korabl’ amethyst deposit, Kola Peninsula. According to the chemical composition, the studied wakefieldite-(Ce) has an average empirical chemical formula of (Ce_0.43Nd_0.19La_0.16Ca_0.10Pr_0.05Y_0.04Sm_0.03)_1.00(V_0.89Fe_0.05P_0.04)_0.98O₄. The relationships between wakefieldite-(Ce) and REE-phosphates indicate the following sequence of mineral formation: monazite-(Ce) → wakefieldite-(Ce) → rhabdophane-(Ce). The mineral paragenesis [hydrothermal hematite, K-feldspar, rare earth element (REE) phosphates] and chemical features of the minerals in the association (REE distribution, elevated content of SO₃ and Cl) indicate a very high degree of oxidation of the hydrothermal solutions with significant activity of K, P and S. It is assumed that the vanadium-bearing solutions were essentially chloride-aqueous, and the source of vanadium was authigenic pore hematite from the red sandstones hosting the veins.

Nb-Ta-Ti-REE (rare earth elements) oxide minerals can serve as petrogenetic indicators in geology, potential materials for nuclear waste immobilization, phosphors for luminescent applications, and other advanced material science uses. The disorder and thermal recovery of their crystal structures are critical properties that determine their suitability for these applications. This study focuses on the metamict fergusonite-(Y) from the Ilmeny Mountains in Russia, which contains inclusions of metamict samarskite-(Y), monazite, xenotime, apatite, and ThSiO₄. To investigate the metamict state, degree of alteration, and thermal recovery of these minerals, we employed scanning electron microscopy (SEM), electron probe micro-analyser (EPMA), Raman spectroscopy, and cathodoluminescence spectroscopy. The fergusonite-(Y) grain, containing mineral inclusions, exhibits variations in chemical composition across grain and pore boundaries, attributed to dissolution-reprecipitation processes under the influence of fluids. Annealing of fergusonite-(Y) at 1250 °C resulted in the formation of β-fergusonite, while the chemical composition remained unchanged. In contrast, samarskite-(Y) transformed into a crystalline state after annealing at 1250 °C, with a compositional shift towards pyrochlore. Our findings demonstrate that fergusonite-(Y) exhibits greater compositional stability compared to samarskite-(Y) under thermal treatment. These results highlight the potential of Nb-Ta-Ti-REE oxide minerals for applications requiring thermal and chemical stability.

Mafic granulites and charnockitic rocks constitute a notable litho-association of the Eastern Ghats Province (EGP), India. The mafic granulites containing abundant hydrous minerals (hornblende and/or biotite), designated as hornblende granulites and hornblende-biotite granulites; whereas, those with dominantly anhydrous assemblages, are the two-pyroxene granulites. Based on the textural and compositional attributes, the hornblende present in such hydrous and anhydrous assemblages are typified as type-I and type-II respectively. Type-I hornblende containing pyroxene and plagioclase at their embayed margins has relatively higher TiO₂ and K₂O contents. Towards their rims, subtle Mg enrichment and Ti depletion (consistent with the formation of opaque oxides along the hornblende margin) are noteworthy. Such signatures show coherence with hornblende dehydration melting thereby indicating prograde hornblende breakdown. The type-II hornblende, forming partial rims on orthopyroxene, has relatively lower TiO₂ and K₂O contents. These are interpreted as hydration products of pyroxenes owing to retrogression. As assessed from pseudosection modelling, the suprasolidus peak assemblage of type-I hornblende-bearing mafic granulite is stable at mid-crustal depths (7.4 kbar), between 789℃ and 984℃. The hornblende granulite represents the mafic residue after extraction of melt (probably the enclosing charnockite) during anatexis. Assuming the coexistence of mafic granulite-charnockite, the rare earth element (REE) content of quantitative model 10% equilibrium batch melt on an N-MORB (normal mid-ocean ridge basalts) like source, using the modal composition of the restitic mafic assemblage, is comparable to the enclosing charnockite. These findings contribute to understanding the presence of prograde and retrograde hornblende within the mafic granulites of EGP and also shed light on the granulite-charnockite relation.

In this paper, we describe a non-invasive method of diamond identification that exploits intrinsic defects of natural crystals embedded into the crystal lattice during their formation. The inevitable lattice defects manifest themselves through the spectral dependence of light absorption in the mid-IR region of the optical spectrum. By collecting multiple spectral data taken from different parts of the diamond sample, followed by the data analysis using methods of deep machine learning, we are able to identify spectral markers associated with otherwise unique lattice defect pattern. The core of the proposed method is a neural network trained on a number of samples belonging to the same class. The class could be multiple measurements of the same diamond or gemstones of the same geographical origin. We demonstrate that the trained neural network is able to identify previously untested samples and to correctly predict their origin. Results of our study suggest that the underlying diamond property allowing its identification is ever-present native defects in the lattice. The three-dimensional pattern of defects, set by temperature, pressure, and their gradients in both time and space during crystal formation, appears to hold information about diamond identity, including its origin. In many aspects, it resembles genomics in living cells. Our results suggest that each diamond mine is associated with a unique set of spectral markers that can be used for cost-effective and potentially very fast non-invasive identification of diamond origin.

The mineralogical and spectroscopic constraints on gem-quality chalcedony-rich bodies from South Khorasan Province (Eastern Iran) were provided to determine their origin and colouration mechanisms. Four distinctive colour varieties, i.e. (I) green, (II) bluish, (III) composite brownish-violet and white, and (IV) nearly colourless with discrete agate banding, were analysed using Raman (RS), Fourier-transform infrared (FTIR), and optical absorption spectroscopy, supported by cathodoluminescence (CL) microscopy and X-ray powder diffraction (XRPD). Type-I was formed via in-situ silicification (birbiritization) of a serpentinized ultramafic protolith (Cretaceous Birjand ophiolite), while other species (type II-IV), hosted by Cenozoic andesitic rocks, originated from post-volcanic hydrothermal activity. The green colour of type-I chalcedony was facilitated by minute Cr-bearing phyllosilicates (possibly smectite-group) that give a specific absorption at 683 nm in the optical absorption spectrum. The bluish hue of chalcedony (type-II) is attributed to light scattering effects enhanced by moganite enrichment, whilst brownish-violet colour (type-III) results from the presence of inclusions (e.g. hematite, carbonaceous material, and dolomite), as well as the possible presence of Fe-related colour centres typical of amethyst. Meanwhile, white regions recognized in both type-II and type-III chalcedony are rich in discrete sepiolite-palygorskite inclusions and/or comprise a peculiar “transitional” phase with a mixed spectroscopic signature of opal, α-quartz, and moganite, as well as a low crystallinity index (CI) of quartz of 1.30. This phase highlights an ongoing textural maturation of amorphous silica. Colourless chalcedony (type-IV) features the peculiar opal-CT-rich layer at the boundary with host andesite. Furthermore, the opal encloses abundant zeolite-group species (Na-heulandite/Na-clinoptilolite) that not only exhibits an unusual bluish-green CL emission, but also formed due to the interactions of agate-forming fluid with the groundmass of volcanic rock.