Volume 106, Issue 11

δ-AlOOH has emerged as a promising candidate for water storage in the lower mantle and could have delivered water into the bottom of the mantle. To date, it still remains unclear how the presence of iron affects its elastic, rheological, vibrational, and transport properties, especially across the spin crossover. Here, we conducted high-pressure X‑ray emission spectroscopy experiments on a δ-(Al 0.85 Fe 0.15 ) OOH sample up to 53 GPa using silicone oil as the pressure transmitting medium in a diamond-anvil cell. We also carried out laser Raman measurements on δ-(Al 0.85 Fe 0.15 )OOH and δ-(Al 0.52 Fe 0.48 )OOH up to 57 and 62 GPa, respectively, using neon as the pressure-transmitting medium. Evolution of Raman spectra of δ-(Al 0.85 Fe 0.15 )OOH with pressure shows two new bands at 226 and 632 cm −1 at 6.0 GPa, in agreement with the transition from an ordered ( P 2 1 nm ) to a disordered hydrogen bonding structure ( Pnnm ) for δ-AlOOH. Similarly, the two new Raman bands at 155 and 539 cm −1 appear in δ-(Al 0.52 Fe 0.48 )OOH between 8.5 and 15.8 GPa, indicating that the incorporation of 48 mol% FeOOH could postpone the order-disorder transition upon compression. On the other hand, the satellite peak ( K β′) intensity of δ-(Al 0.85 Fe 0.15 )OOH starts to decrease at ~30 GPa and it disappears completely at 42 GPa. That is, δ-(Al 0.85 Fe 0.15 )OOH undergoes a gradual electronic spin-pairing transition at 30–42 GPa. Furthermore, the pressure dependence of Raman shifts of δ-(Al 0.85 Fe 0.15 )OOH discontinuously decreases at 32–37 GPa, suggesting that the improved hydrostaticity by the use of neon pressure medium could lead to a relatively narrow spin crossover. Notably, the pressure dependence of Raman shifts and optical color of δ-(Al 0.52 Fe 0.48 )OOH dramatically change at 41–45 GPa, suggesting that it probably undergoes a relatively sharp spin transition in the neon pressure medium. Together with literature data on the solid solutions between δ-AlOOH and ε-FeOOH, we found that the onset pressure of the spin transition in δ-(Al,Fe)OOH increases with increasing FeOOH content. These results shed new insights into the effects of iron on the structural evolution and vibrational properties of δ-AlOOH. The presence of FeOOH in δ-AlOOH can substantially influence its high-pressure behavior and stability at the deep mantle conditions and play an important role in the deep-water cycle.

While much progress has been made in electron-probe microanalysis (EPMA) to improve the accuracy of point analysis, the same level of attention has not always been applied to the quantification of wavelength-dispersive spectrometry (WDS) X-ray intensity maps at the individual pixel level. We demonstrate that the same level of rigor applied in traditional point analysis can also be applied to the quantification of pixels in X-ray intensity maps, along with additional acquisition and quantitative processing procedures to further improve accuracy, precision, and mapping throughput. Accordingly, X-ray map quantification should include pixel-level corrections for WDS detector deadtime, corrections for changes in beam current (beam drift), changes in standard intensities (standard drift), high-accuracy removal of background intensities, quantitative matrix corrections, quantitative correction of spectral interferences, and, if required, time-dependent corrections (for beam and/or contamination sensitive materials). The purpose of quantification at the pixel level is to eliminate misinterpretation of intensity artifacts, inherent in raw X-ray intensity signals, that distort the apparent abundance of an element. Major and minor element X-ray signals can contain significant artifacts due to absorption and fluorescence effects. Trace element X-ray signals can contain significant artifacts where phases with different average atomic numbers produce different X-ray continuum (bremsstrahlung) intensities, or where a spectral interference, even an apparently minor one, can produce a false-positive intensity signal. The methods we propose for rigorous pixel quantification require calibration of X-ray intensities on the instrument using standard reference materials, as we already do for point analysis that is then used to quantify multiple X-ray maps, and thus the relative time overhead associated with such pixel-by-pixel quantification is small. Moreover, the absolute time overhead associated with this method is usually less than that required for quantification using manual calibration curve methods while resulting in significantly better accuracy. Applications to geological, synthetic, or engineering materials are numerous as quantitative maps not only show compositional 2D variation of fine-grained or finely zoned structures but also provide very accurate quantitative analysis, with precision approaching that of a single point analysis, when multiple-pixel averaging in compositionally homogeneous domains is utilized.

In this paper, we report a first-principles Molecular Dynamics (FPMD) study of interfacial structures and acidity constants of goethite. The p K a values of the groups on (010), (110), and (021) surfaces (space group Pbnm ) are derived with the FPMD based vertical energy gap technique. The results indicate that major reactive groups include ≡Fe 2 OH 2 and ≡FeOH 2 on (010), ≡FeOH 2 , ≡Fe 3 O L H, and ≡Fe 3 O U H on (110), and ≡FeO h H 2 and ≡Fe 2 OH on (021). The interfacial structures were characterized in detail with a focus on the hydrogen bonding environment. With the calculated p K a values, the point of zero charges (PZCs) of the three surfaces are derived and the overall PZC range of goethite is found to be consistent with the experiment. We further discuss the potential applications of these results in future studies toward understanding the environmental processes of goethite.

Sound velocities of iron and iron-based alloys at high pressure and high temperature are crucial for understanding the composition and structure of Earth’s and other telluric planetary cores. In this study, we performed ultrasonic interferometric measurements of both compressional ( v P ) and shear ( v S ) velocities on a polycrystalline body-centered-cubic (bcc)-Fe 90 Ni 10 up to 8 GPa and 773 K. The elastic moduli and their pressure and temperature derivatives are derived from least-square fits to third-order finite strain equations, yielding K S0 = 154.2(8) GPa, G 0 = 73.2(2) GPa, K S ′ 0 = 4.6(2), G 0 ′ = 1.5(1), ∂K S /∂ T = –0.028(1) GPa/K, and ∂G/∂ T = –0.023(1) GPa/K. A comparison with literature data on bcc-Fe suggests that nickel not only decreases both P and S wave velocities but also weakens the temperature effects on the elastic moduli of Fe-Ni alloys.

Studies of the new growth and re-distribution of Cu-rich phases in chondrites of different petrologic subtypes can potentially provide insights into post-accretionary parent-body processes. We present a systematic study of the distribution of Cu-rich phases and metallic Cu in Ornans-like carbonaceous chondrites (CO3) that underwent little aqueous alteration or shock (most with shock stages of S1) but exhibit a range of thermal metamorphism (subtype 3.0–3.7). A comparison to ordinary chondrites (OCs), which have undergone a larger range of shock levels, allows us to constrain the relative roles of radiogenic and shock heating in the origin of Cu distribution in chondrites. We found that the Cu content of Ni-rich metal and calculated bulk Cu content of CO3 chondrites (based on mass-balance calculations) show an increase from CO3.0 to CO3.2 chondrites. We speculate that some unidentified phases in the matrix account for a significant portion (nearly ~100 ppm) of the Cu budget in bulk samples of CO3.0 chondrites, while Ni-rich metal is the main Cu-carrier for CO3.2–3.7 chondrites. Within CO3.2–3.7 chondrites, Cu and Ni contents of Ni-rich metal are positively correlated, showing a systematic decrease from lower to higher subtype (~0.41 wt% Cu and ~45.0 wt% Ni in CO3.2 Kainsaz; ~0.28 wt% Cu and ~38.8 wt% Ni in CO3.7 Isna). Metallic Cu grains were found in every sample of CO3.2–3.7 chondrites, but not in any CO3.0–3.1 chondrites. Metallic Cu is: (1) present at metallic-Fe-Ni-pyrrhotite interfaces; (2) associated with fine irregular pyrrhotite grains in Ni-rich-metal-pyrrhotite nodules; (3) associated with fizzed pyrrhotite (fine-grained mixtures of irregularly shaped metal grains surrounded by pyrrhotite); (4) present at the edges of metallic Fe-Ni grains; and (5) present as isolated grains. In some metallic-Cu-bearing mineral assemblages, pyrrhotite has higher Cu concentrations than adjacent Ni-rich metal and shows a drop in Cu concentration at the interface between metallic Cu and Cu-rich pyrrhotite. This implies that the precipitation of metallic Cu grains could be related to the local Cu enrichment of pyrrhotite. We consider that radiogenic heating is mainly responsible for the formation of opaque phases in CO chondrites based on the relatively slow metallographic cooling rate (~0.1–5 °C/Ma), the increasing uniformity of Ni contents in Ni-rich metal with increasing CO subtype (44.3 ± 17.3 wt% in CO3.00 to 38.8 ± 3.4 wt% in CO3.7 chondrite), and the relatively narrow range of pyrrhotite metal/sulfur ratios (~0.976–0.999). Metal/sulfur ratios of pyrrhotite grains in most CO3.2–3.7 chondrites (mean = ~0.986–0.997; except Lancé) are slightly higher than those in CO3.0–3.1 chondrites (mean = ~0.981–0.987; except Y-81020), possibly indicative of a release and re-mobilization of sulfur during progressive heating as previously reported for type-3 chondrites. In this regard, we suggest most metallic Cu grains in CO3 chondrites may have precipitated from Cu-rich pyrrhotite due to sulfidation of Fe-Ni metal during parent-body thermal metamorphism. Locally, a few metallic Cu grains associated with fizzed pyrrhotite could have formed during transient shock-heating. Both thermal and shock metamorphism could be responsible for the formation of metallic Cu. Although the systematic decrease in the Ni contents of Ni-rich metal from subtype-3.2 to subtype-3.8 also occurs in OCs, the average Cu contents of Ni-rich metal grains are indistinguishable among type-3 OCs of different subtypes. The paucity of metallic Cu in weakly shocked type-3 OCs could be related to: (1) the relatively low-bulk Cu contents of OCs, and/or (2) the relatively rapid metallographic cooling rates at <500–600 °C (~1–10 °C/Ma for LL chondrites), possibly resulting from early disturbance of OC parent bodies. The intergrowth of metallic Cu and irregular pyrrhotite more commonly occurs in shocked type-4 to type-6 OCs than in CO3 chondrites. This could be due to S in type-4 to type-6 OCs being more mobilized due to shock heating than in unshocked CO3 chondrites. We predict that some other groups of carbonaceous chondrites (e.g., CI and CM) are less likely to produce metallic Cu due to the: (1) relatively low amount of metallic Fe-Ni; (2) relatively low parent-body temperatures of ~100–300 °C; (3) high mobility of Cu in solution for aqueously altered samples; and (4) the short heating duration for metamorphosed samples.

Spectral features of hydrogen defects in natural mantle minerals derive from physico-chemical conditions of the lithosphere. Although hydrogen defects in synthetic orthopyroxene have been well investigated, their complex spectral features in natural orthopyroxenes are still difficult to decipher. To clarify this issue, it is indispensable to reveal what happens to hydrogen defects during high-temperature processes, thereby fingerprinting the origins of hydrogen defects observed in natural orthopyroxene. Here, we carry out Fourier transform infrared spectroscopic studies on hydrogen defects of three natural orthopyroxenes at elevated temperatures to 1000 °C. Hydrogen defects display reversible disordering at temperatures above 700 °C, which is diferent from those at ambient conditions. Moreover, hydrogen diffusivities are significantly different between the orthopyroxene samples from diferent tectonic settings despite their similar iron contents. Even for the same crystal, different hydrogen defects display diferent difusion behaviors. Hydrogen defects corresponding to the 3420 cm −1 band have the fastest diffusivity relative to the other hydrogen defects. Most importantly, hydrogen defects can redistribute in the crystal, with new hydrogen defects produced at the cost of the initial hydrogen defects rather than involving a reaction with an external hydrogen source. Combining these findings with previously reported hydrogen defects in natural olivine and clinopyroxene at high temperatures, we propose that: (1) to correctly relate hydrogen defects features to geological processes, it is imperative to understand their behavior and origin, and (2) hydrogen disordering should be taken into account when predicting and extrapolating data on physical properties of the mantle from room-temperature measurements.

The transport of calcium carbonate (CaCO 3 ) into the Earth’s interior through subduction is one of the key processes in the global cycling of carbon. To develop a better understanding of the CaCO 3 structural stability during subduction processes, the phase transitions among CaCO 3 -I (calcite), CaCO 3 - II, -III/IIIb, and aragonite under pressure-temperature ( P-T ) conditions up to 2.5 GPa and 600 °C, in hydrous and anhydrous environments, were investigated using a hydrothermal diamond-anvil cell. One displacive and two reconstructive processes during the phase transitions among CaCO 3 polymorphs were confirmed from the results obtained from in situ observations and Raman spectroscopic measurements. Meanwhile, the efect of Ca-substitutional metal cations (e.g., Mg 2+ ) in CaCO 3 and the presence of an aqueous fluid on the phase transition processes have been determined. Specifically, the CaCO 3 -I ↔ -II phase transition is a displacive process, occurring instantly at pressures varying from 1.6 GPa at room temperature to 1.5 GPa at 500 °C with the phase equilibrium boundary having a minimum P-T point at ~1.4 GPa at 300 °C, and is completely reversible upon cooling and decompression. The CaCO 3 -II → -III phase transition is a reconstructive process, observed at P-T conditions from 2.0 GPa at room temperature to 2.5 GPa at 150 °C, and is accomplished by solid recrystallization starting from CaCO 3 -II, transitioning through an intermediate CaCO 3 -IIIb, and ending at the CaCO 3 -III structure. The phase transition between CaCO 3 -I or -II and aragonite, which is also a reconstructive process, was found to occur by progressive solid recrystallization under high P-T hydrous and anhydrous conditions, or alternatively, via dissolution-precipitation under low- P-T hydrous conditions, depending on the presence of aqueous fluids and the heating rate of the system. The substitution for Ca 2+ by other metal cations (e.g., Mg 2+ , Mn 2+ , Fe 2+ ) in CaCO 3 results in a significant increase in the pressures for the displacive and solid recrystallization reconstructive phase transitions, but has no detectable influence on the CaCO 3 -I/II ↔ aragonite transformation via a dissolution-precipitation process under hydrous conditions. Our results show that the presence of Ca-substitutional metal cations in CaCO 3 is a key factor controlling the phase stability of CaCO 3 under high P-T conditions, and suggest that aragonite should be the predominant phase in the upper mantle in subduction zones where the heating rate is very low and slab dehydration is prevalent.

Antigorite, a high-pressure polymorph of serpentine, is considered to be the most abundant hydrous mineral in subduction zones. Although antigorite dehydration is presumed as one of the origins of intermediate-depth earthquakes in the subduction zone, the amount of antigorite is uncertain because the amount of water infiltrated into the oceanic lithosphere is still debated. To investigate whether antigorite can be formed even with limited water availability, we conducted the axial deformation experiments of magnesium germanate at 1.2 GPa and T = 500–800 °C using a Griggs-type deformation apparatus. Magnesium germanate is an analog material of magnesium silicate, and the starting material was dried prior to experimentation. Nevertheless, the samples had initially high porosity, and hence a small amount of water (about 200 ppm wt H 2 O) was retained in the samples. In the samples deformed at 600 °C, stable slip occurred, and TEM analysis revealed that fine-grained platelets of germanate antigorite existed along the faults. A sharp absorption band assigned to the OH-stretching vibration of antigorite in Fourier transform infrared spectroscopic (FTIR) analysis also implies that antigorite was formed in the samples deformed at a temperature lower than 600 °C. Our results indicate that strain-induced hydration of germanate olivine results in antigorite formation even with only a small amount of water present. Thus, partial serpentinization in the oceanic lithosphere can occur under slight water infiltration due to the high strain accumulated by subduction.

Fibrous amphibole and clay mineral inclusions that form striking trapiche-like star patterns within quartz crystals from Inner Mongolia, China, present a challenge to uncover how these crystals grow and incorporate inclusions in a geological context. We propose that the patterns formed as a result of protogenic clay (ferrosaponite or nontronite) inclusions that were preferentially trapped on rough surfaces during quartz crystal growth. The rough surface texture of these crystals is the result of multiple growth centers during 2D nucleation and spread and split crystal formation. Observations via optical microscopy, cathodoluminescence, and three-dimensional micro-CT scanning highlight how the exterior surface textures on the termination of a complete quartz crystal mimic its interior inclusion patterns. Cathodoluminescence images, as well as varying aluminum concentrations along a core-to-exterior transect in a quartz crystal slice, suggest that the formation fluid underwent a heterogeneous chemical history. Measurements of Ti and observations of fluid inclusions suggest the quartz formed at a temperature of under 348 °C. This study presents the details surrounding split crystal growth in quartz in a natural geological setting, which has implications for inspiring new materials and may serve as an indicator for turbid and highly supersaturated formation fluid conditions in geological formations.

Gold (Au) deposits have formed in orogenic belts throughout Earth’s history. However, the upper temperature limits of orogenic Au vein formation are difficult to constrain because measurements made on fluid inclusions focus on intermediate to late-stage minerals (e.g., quartz and calcite) or are based on P-T estimates for the metamorphic mineral assemblages of the host rocks. We conducted a study of TiO 2 polymorphs that are among the earliest minerals that grew in Au-bearing veins of the Dongyuan deposit, Jiangnan orogenic Au belt, South China. Based on Raman analyzes, we identified TiO 2 polymorphs of anatase (with Raman peaks at 396, 515, and 638 cm −1 ), rutile (with Raman peaks at 235, 447, and 613 cm −1 ), and anatase–rutile intergrowths. Transmission electron microscope (TEM) confirmed the polymorphs identifying the [11 1] zone axis of anatase, [110] zone axis of rutile, and [11 1] and [111] zone axes of rutile–anatase intergrowths. The TiO 2 polymorphs in the Dongyuan Au veins constrain a temperature range for early mineral precipitation in the veins of 450–550 °C. The results show that ore-forming fluids for this orogenic Au deposit emplaced in the shallow crust originated from deeper and hotter crustal levels (e.g., high-grade metamorphic rocks in the middle to lower crust).

The mobility of Ti, a member of high field strength elements, in metamorphic fluids is crucial to understand the recycling of commonly perceived nominally soluble elements and for mass-flux calculations during crustal processes. In this study, we present evidence for large-scale Ti mobility from a suite of clinohumite±spinel-bearing dolomitic marbles from the Makrohar area in central India. The studied rocks mostly contain dolomite and calcite (in subequal proportions) and a subordinate amount of forsterite. It commonly develops 1–5 cm thick, laterally continuous, mostly parallel, sometimes anastomosing, brown-colored clinohumite rich bands with variable spinel. Clinohumite has moderate Ti and F (TiO 2 = 0.55–2.88 wt%; F = 0.94–1.88 wt%; n = 32). Textural and phase equilibria modeling indicate that clinohumite grew at the expense of forsterite + dolomite under static conditions due to infiltration of F- and Ti-bearing extremely H 2 O-rich fluids (X CO 2 < 0.03), at ~5–6 kbar pressure and ~650–700 °C temperature. The Ti and F were most likely supplied by highly channelized aqueous fluids restricted within the centimeter-thick bands. The negative volume change of the reactions further facilitated fluid ingress. The lateral continuity of the bands over several meters across multiple outcrops indicates that Ti was mobile at the meter to kilometer scale. The results are in accordance with experimental studies that solubility of Ti increases in the presence of halides and imply that Ti may be much more mobile in metamorphic fluids during regional metamorphism than previously anticipated.

Carletonmooreite (IMA 2018-68), Ni 3 Si, is a new nickel silicide mineral that occurs in metal nodules from the Norton County aubrite meteorite. These nodules are dominated by low-Ni iron (kamacite), with accessory schreibersite, nickelphosphide, perryite, and minor daubréelite, tetrataenite, taenite, and graphite. The chemical composition of the holotype carletonmooreite determined by wavelength-dispersive electron-microprobe analysis is (wt%) Ni 82.8 ± 0.4, Fe 4.92 ± 0.09, and Si 13.08 ± 0.08 (n = 6, total = 100.81) giving an empirical formula of (Ni 2.87 Fe 0.18 ) Σ3.05 Si 0.95 , with an end-member formula of Ni 3 Si. Further grains discovered in the specimen after the new mineral submission extend the composition, i.e., (wt%) Ni 81.44 ± 0.82, Fe 5.92 ± 0.93, Cu 0.13 ± 0.02, and Si 13.01 ± 0.1 (n = 11, total = 100.51 ± 0.41), giving an empirical formula (Ni 2.83 Fe 0.22 Cu 0.004 ) Σ3.05 Si 0.95 . The backscattered electron-diffraction patterns were indexed by the Pm 3 m auricupride (AuCu 3 )-type structure and give a best fit to synthetic Ni 3 Si, with a = 3.51(1) Å, V = 43.2(4) Å 3 , Z = 1, and calculated density of 7.89 g/cm 3 . Carletonmooreite is silver colored with an orange tinge, isotropic, with a metallic luster and occurs as euhedral to subhedral crystals 1 × 5 μm to 5 × 14 μm growing on tetrataenite into kamacite. The dominant silicide in the Norton County aubrite metal nodules is perryite (Ni,Fe) 8 (Si,P) 3 , with carletonmooreite restricted to localized growth on rare plessite fields. The isolated nature of small euhedral carletonmooreite single crystals suggests low-temperature growth via solid-state diffusion from the surrounding kamacite and epitaxial growth on the tetrataenite. This new mineral is named in honor of Carleton B. Moore, chemist and geologist, and founding director of the Center for Meteorite Studies at Arizona State University, for his many contributions to cosmochemistry and meteoritics.

The concentration of sulfur that can be dissolved in a silicate liquid is of fundamental importance because it is closely associated with several major Earth-related processes. Considerable effort has been made to understand the interplay between the efects of silicate melt composition and its capacity to retain sulfur, but the dependence on pressure and temperature is mostly based on experiments performed at pressures and temperatures below 6 GPa and 2073 K. Here we present a study of the effects of pressure and temperature on sulfur content at sulfide saturation of a peridotitic liquid. We performed 14 multi-anvil experiments using a peridotitic starting composition, and we produced 25 new measurements at conditions ranging from 7 to 23 GPa and 2173 to 2623 K. We analyzed the recovered samples using both electron microprobe and laser ablation ICP-MS. We compiled our data together with previously published data that were obtained at lower P-T conditions and with various silicate melt compositions. We present a new model based on this combined data set that encompasses the entire range of upper mantle pressure-temperature conditions, along with the efect of a wide range of silicate melt compositions. Our findings are consistent with earlier work based on extrapolation from lower-pressure and lower-temperature experiments and show a decrease of sulfur content at sulfide saturation (SCSS) with increasing pressure and an increase of SCSS with increasing temperature. We have extrapolated our results to pressure-temperature conditions of the Earth’s primitive magma ocean, and show that FeS will exsolve from the molten silicate and can efectively be extracted to the core by a process that has been termed the “Hadean Matte.” We also discuss briefly the implications of our results for the lunar magma ocean.

A new mineral of the beryl group, johnkoivulaite, Cs(Be 2 B)Mg 2 Si 6 O 18 , was recovered from the gem gravels in the Pein Pyit area of the Mogok region in Myanmar. Thus far, only a single crystal has been identified. It has dimensions of about 5.8 × 5.7 × 5.5 mm. This specimen has an irregular shape but still has discernible crystal form with geometric growth patterns observed on the crystal faces. The crystal of johnkoivulaite is grayish-violet in color and strongly pleochroic, going from nearly colorless with E┴ c to dark bluish-violet with E|| c . Johnkoivulaite has a Mohs hardness of about 7½ and a measured density of 3.01(10) g/cm 3 . It is uniaxial (–) with ω = 1.607(1) and ε = 1.605(1) (white light). Electron microprobe analyses gave the empirical formula of (Cs 0.85 K 0.10 Na 0.01 )(Be 1.88 B 1.12 )(Mg 1.66 Fe 0.27 Mn 0.01 Al 0.05 ) (Si 5.98 )O 18 with Be calculated by stoichiometry and confirmed by LA-ICP-MS measurements. Johnkoivulaite is hexagonal, P 6/ mmc (no. 192) with a = 9.469(2), c = 9.033(2) Å, V = 701.5(3) Å 3 , and Z = 2. Johnkoivulaite is isostructural with beryl and exhibits partial substitution of B for Be at the distorted tetrahedral site, Mg for Al at the octahedral site, and Cs in the channel sites within the stacked Si 6 O 18 rings. This substitution can be written as (CsMg 2 B)(□Al 2 Be) –1 . Johnkoivulaite, the seventh member of the beryl group, is named in honor of gemologist John Koivula in recognition of his contributions to mineralogy and gemology.

The Mogok metamorphic belt (MMB), Myanmar, is one of the most well-known gemological belts on Earth. Previously, 40 Ar/ 39 Ar, K-Ar, and U-Pb dating have yielded Jurassic-Miocene magmatic and metamorphic ages of the MMB and adjacent areas; however, no reported age data are closely related to the sapphire and moonstone deposits. Secondary ion mass spectrometry (SIMS) U-Pb dating of acicular rutile inclusions in sapphire and furnace step-heating 40 Ar/ 39 Ar dating of moonstone (antiperthite) in syenites from the MMB yield ages of 13.43 ± 0.92 and 13.55 ± 0.08 Ma, respectively, indicating both Myanmar sapphire and moonstone formed at the same time, and the ages are the youngest published in the region. The ages provide insight into the complex histories and processes of magmatism and metamorphism of the MMB, the formation of gemstone species in this belt, and the collision between India and Asia. In addition, our high field strength element data for the oriented rutile inclusions suggest an origin by co-precipitation rather than exsolution. In situ age determination of this nature is particularly significant since rutile inclusions in other gemstones, such as rubies, can be used to help constrain the geological history of their host rocks elsewhere.

X‑ray computed microtomography (CT) of impact rock varieties from the Kara astrobleme is used to test the method’s ability to identify the morphology and distribution of the rock components. Three types of suevitic breccias, clast-poor melt rock, and a melt clast from a suevite were studied with a spatial resolution of 24 μm to assess CT data values of 3D structure and components of the impactites. The purpose is first to reconstruct pore space, morphology, and distribution of all distinguishable crystallized melt, clastic components, and carbon products of impact metamorphism, including the impact glasses, after-coal diamonds, and other carbon phases. Second, the data are applied to analyze the morphology and distribution of aluminosilicate and sulfide components in the melt and suevitic breccias. The technical limitations of the CT measurements applied to the Kara impactites are discussed. Because of the similar chemical composition of the aluminosilicate matrix, glasses, and some lithic and crystal clasts, these components are hard to distinguish in tomograms. The carbonaceous matter has absorption characteristics close to air, so the pores and carbonaceous inclusions appear similar. However, X‑ray microtomography could be used to prove the differences between the studied types of suevites from the Kara astrobleme using structural-textural features of the whole rock, porosity, and the distributions of carbonates and sulfides.