Coprecipitation of phosphate in calcium carbonate minerals is a ubiquitous geochemical phenomenon in marine sedimentation and cave stalagmite formation, however, it is not clear whether phosphate is incorporated into the calcite structure. In this research, we applied solid-state nuclear magnetic resonance (NMR) spectroscopy to analyze P speciation during coprecipitation with calcite. The 31P NMR results show three peaks with chemical shifts of 3.9, 3.0 and-1.0 ppm, indicative of at least three phosphate species in the coprecipitates. Combined with advanced 31P{1H} cross-polarization (CP)/MAS, 1H DE/MAS, 31P{1H} 2-d heteronuclear correlation (HetCor) and 31P{13C} cross-polarization rotational echo double resonance (CP-REDOR) NMR experiments, the 3.9 ppm peak can be tentatively assigned to calcite structural defects as amorphous calcium phosphate (ACP)-like environments while the 3.0 ppm peak arises from a carbonated hydroxyapatite (CHap). The 31P NMR peak at-1.0 ppm can be assigned to structurally incorporated phosphate in the calcite crystals in the form of HPO42-. Nano secondary ion mass spectrometry (NanoSIMS) and high-resolution scanning transmission electron microscopy (HR-STEM) analysis further suggests that the incorporated HPO42-substitutes for the structural carbonate group (CO32-) of calcite. However, the local expansion stress field generated with HPO42-incorporation in the calcite structure prevents PO4/CO3 isomorphous substitution and favors the precipitation of calcium phosphates. The findings of this study not only provide deep insights into carbonate crystal chemistry but also shed light on the application of carbonate materials as potent geochemical proxies in paleoenvironmental reconstructions.

Rare earth elements (REEs) are critical minerals that are indispensable for the clean energy transition. Understanding their occurrence and behavior in highly weathered environments provides valuable insights into the identification and prediction of potential REE resources. Phosphate (P) plays an important role in controlling the geochemical behaviors of REE during weathering and secondary deposition. REE-phosphate minerals, such as monazite and xenotime, are among the important natural sources of REE. However, the molecular-scale reaction mechanisms underlying phosphate-REE interactions in weathering environments remain unclear. This study investigates the interaction between phosphate and yttrium on the surface of kaolinite, a representative and abundant clay mineral in highly weathered environments. At circumneutral pH 6, phosphate inhibits yttrium mobilization by forming ternary kaolinite-yttrium-phosphate complexes and surface precipitation. The reaction mechanisms identified in this study are distinct from previously reported adsorption-dominated processes on clay minerals that govern REE immobilization during chemical weathering. Solid-state nuclear magnetic resonance (NMR) spectroscopy, including 31P direct polarization magic angle spinning (DP/MAS) and 1H - 31P cross polarization (CP) rotational echo adiabatic passage double resonance (REAPDOR) analyses, provides direct molecular-scale evidence for the yttrium-phosphate surface complexation on kaolinite. Quantification of atomic distances by numerical simulations further substantiates the formation of ternary surface complexes. These mechanistic findings enhance our understanding of phosphate-mediated REE mobilization, transport, and redeposition in natural environments.

The early‐middle Neoproterozoic is thought to have witnessed significant perturbations to marine P cycling, in turn facilitating the rise of eukaryote‐dominated primary production. However, with few robust constraints on aqueous P concentrations, current understanding of Neoproterozoic P cycling is generally model‐dependent. To provide new geochemical constraints, we combined microanalytical data sets with solid‐state Nuclear Magnetic Resonance, synchrotron‐based X‐ray Absorption Near Edge Structure spectroscopy, and micro‐X‐ray Fluorescence imaging to characterize the speciation and distribution of P in Tonian shallow‐water carbonate rocks. These data reflect shallow water phosphate concentrations 10–100× higher than modern systems, supporting the hypothesis that tectonically‐driven influxes in P periodically initiated kinetically‐controlled CaCO 3 deposition, in turn destabilizing marine carbonate chemistry, climate, and nutrient inventories. Alongside these observations, a new compilation and statistical analysis of mudstone geochemistry data indicates that, in parallel, C org and P burial increased across later Tonian continental margins until becoming decoupled at the close of the Tonian, implicating widespread N‐limitation triggered by increasing atmospheric O 2 .

The boron isotope composition for boron incorporated in marine calcium carbonate minerals has become an increasingly important proxy for seawater pH and thus a key constraint for the concentration of atmospheric carbon dioxide in the geologic past. We report here the results of a solid-state NMR study undertaken to investigate the nature of the boron substitution in calcite and its relationship to the calcite structure. Calcite/boron coprecipitates with B concentrations ranging from 149 to 1260 mu g/g were prepared using the constant rate of addition method with 99% C-13-carbonate to facilitate the application of double-resonance NMR techniques. The B-11 MAS/NMR spectra indicate the presence of both three-coordinated (B(3)) and four-coordinated boron (B(4)) in all of the synthetic samples, with subequal abundances. Strong dephasing effects were observed in B-11-observed/C-13 rotational-echo double-resonance (REDOR) experiments for both B(3) and B(4), indicating that both types of coordination environment occur in the calcite structure and in atomically close proximity to carbonate groups. The variation in the REDOR spectra with dephasing time for the sample with the highest B content reveals the presence of two distinct trigonal B environments that differ principally in the quadrupolar asymmetry parameter (eta). Only the asymmetric B(3) (eta congruent to 0.65) occurs in the REDOR difference spectra and can be assigned to calcite-hosted boron. The signal from an axially symmetric trigonal environment (eta congruent to 0) dominates the dephased REDOR spectra at intermediate dephasing times and exhibits rapid spin-spin relaxation, suggesting assignment to B[OH](3) groups external to calcite. The symmetric B(3) accounts for similar to 15% of the B for samples with the highest B content but appears to be much less abundant or absent in samples with a lower B content, including modern and fossil brachiopods. Model-free decomposition of the B-11 spin-echo spectra corroborates this interpretation of the REDOR results. Comparison of the NMR parameters calculated in a previous study with those measured for B(4) and the asymmetric B(3) indicates assignment, respectively, to B[OH](4)(-) and BO2[OH](2-) groups in calcite. These results are consistent with the incorporation of trigonal B in calcite during coprecipitation but inconclusive as to whether it results from deprotonation of boric acid or coordination change of the borate ion through deprotonation and hydroxyl transfer reactions. In either case, incorporation of trigonal B must involve multiple hydrolytic processes at the calcite/fluid interface during crystal growth, which converge to yield a surprisingly structurally homogeneous B(3) substitution.

Coral reefs and their ecosystems are threatened by both global stressors, including increasing sea-surface temperatures and ocean acidification (OA), and local stressors such as land-based sources of pollution that can magnify the effects of OA. Corals can physiologically control the chemistry of their internal calcifying fluids (CF) and can thereby regulate their calcification process. Specifically, increasing aragonite saturation state in the CF (ΩCF) may allow corals to calcify even under external low saturation conditions. Questions remain regarding the physiological processes that govern the CF chemistry and how they change in response to multiple stressors. To address this knowledge gap, the boron δ11B and B/Ca were analyzed in tropical corals, Porites lobata, collected at submarine groundwater seeps impacted by the release of treated wastewater in west Maui, Hawai'i, to document the interactions between high nutrient / low pH seep water on CF carbonate chemistry. Results show substantial up-regulation of pH and dissolved inorganic carbon (DIC) with respect to seawater in P. lobata corals collected from within the wastewater impacted area at Kahekili Beach Park compared to the control site at Olowalu Beach. The ΩCF was 9 to 10 times higher than ambient seawater Ω, and 13 to 26% higher than in corals from the control site and from values previously observed in tropical Porites spp. corals. Such elevated up-regulation suggests that corals exposed to nutrient-enriched, low pH effluent sustain CF supersaturated with respect to aragonite, possibly as an internal coping mechanism to combat multiple stressors from land-based sources of pollution. This elevated up-regulation has implications to coral vulnerability to future climate- and ocean-change.

Abstract Constraints on marine phosphate availability and cycling directly inform our understanding of long‐term biological evolution. However, early Earth phosphate records are sparse, biased toward siliciclastic samples, and susceptible to post‐depositional modification. Well‐preserved shallow marine inorganic carbonate precipitates provide a complementary yet understudied record of phosphate cycling. We combined micro‐X‐ray fluorescence mapping, X‐ray absorption, and Nuclear Magnetic Resonance spectroscopy on samples of Precambrian syndepositional herringbone calcite (HBC) and microspar to characterize phosphorus speciation and distribution in these carbonate fabrics. Phosphorus spectroscopy from synthetic calcite, HBC, and microspar, is qualitatively consistent with a disordered distribution of phosphate. These characteristics are diagnostic of calcite‐hosted phosphate, which is pervasive at low concentrations in HBC and microspar. This study provides evidence that ancient, well‐preserved carbonate fabrics retain phosphate sourced from seawater and highlights the potential for an unaltered archive of marine phosphate concentration over geologic time.

Variscite [Al(PO4)center dot 2H(2)O] is an uncommon secondary phosphate mineral but is important in a variety of environmental and technological applications. It exists in at least one monoclinic (metavariscite) and two orthorhombic polymorphs ("Lucin-type" and "Messbach-type"), but the fine-grained nature of the "Messbach-type" variscite has hampered the determination of its crystal structure. The crystal structure of the latter from Tooele County, Utah, was solved and refined using laboratory powder X-ray diffraction (XRD) data, charge-flipping, and the Rietveld method. Both variscite modifications belong to the family of framework 3D MT structures in which octahedra (M) and tetrahedra (T) are linked by bridging O atoms. Topological analysis reveals that the two structures are polytypes. Based on our results and our structural interpretations, we refer to "Lucin-type" variscite as variscite1O and the "Messbach-type" as variscite20, to be consistent with modern polytype terminology. The similarity of these two structures suggests that 10-20 interstratifications may exist in nature, which is consistent with observed broadening of diffraction peaks of the Tooele material. 31 P and 27 Al MAS/NMR measurements are consistent with the XRD-determined crystal structure, and they show distinct signals for each of the two independent P and Al positions in variscite20. High-temperature XRD, thermal analyses, and NMR measurements were applied to study the nature of the transformation of variscite20 to a derivative AlPO4 structure above 473 K. Charge-flipping analysis showed that the crystal structure of the new anhydrous AlPO4 phase (AlPO4 -var20 in analogy to its parent structure) can be described as a 3D framework of alternating AlO4 and PO4 tetrahedra linked by bridging O atoms. Thermogravimetric analyses revealed almost complete dehydration above similar to 450 K, and NMR results were consistent with tetrahedral Al and P atoms.

We report a synthetic pathway by which amorphous Al(OH)(3) is converted to.-AlOOH through hydrothermal reaction in the presence of water at temperature T = 473 K. X-ray pair distribution function measurements reveal that the initially amorphous Al(OH)(3) possesses a locally gamma-Al(OH)(3)-like structure, while nanocrystalline gamma-AlOOH precipitates within 1 h of continuous hydrothermal exposure. Solid state nuclear magnetic resonance measurements show that resonant features associated with four- and five-member Al clusters persist through 20 min of hydrothermal treatment, and ultraviolet (UV) spectra mark the onset of UV-induced photoluminescent features characteristic to gamma-AlOOH with 10 min of exposure, indicating a coexistence region of gamma-Al(OH)(3)-like and gamma-AlOOH-like amorphous species. Powder x-ray diffraction measurements of desiccated powders reveal that the conversion process takes place in distinct, power law-defined stages with initial gamma-AlOOH nucleation occurring within the first 20 min, followed by a similar to 1 h period of rapid grain coarsening and the subsequent onset of Lifshitz-Slyozov-Wagner-like coalescence.

As part of an effort to characterize clusters and intermediate phases likely to be encountered along solution reaction pathways that produce iron and aluminum oxide-hydroxides from Fe and Al precursors, the complete structure of Al10O14(OH)2 (akdalaite) was determined from a combination of single-crystal X-ray diffraction (SC-XRD) data collected at 100 K to define the Al and O positions, and solid-state nuclear magnetic resonance (NMR) and neutron powder diffraction (NPD) data collected at room temperature (~300 K) to precisely determine the nature of hydrogen in the structure. Two different synthesis routes produced different crystal morphologies. Using an aluminum oxyhydroxide floc made from mixing AlCl3 and 0.48 M NaOH, the product had uniform needle morphology, while using nanocrystalline boehmite (Vista Chemical Company Catapal D alumina) as the starting material produced hexagonal plates. Akdalaite crystallizes in the space group P63mc with lattice parameters of a = 5.6244(3) Å and c = 8.8417(3) Å (SC-XRD) and a = 5.57610(2) Å and c = 8.77247(6) Å (NPD). The crystal structure features Al13O40 Keggin clusters. The structural chemistry of akdalaite is nonideal but broadly conforms to that of ferrihydrite, the nanomineral with which it is isostructural.

Carbonate glasses can be formed routinely in the system K 2 CO 3 –MgCO 3 . The enthalpy of formation for one such 0.55K 2 CO 3 –0.45MgCO 3 glass was determined at 298 K to be 115.00 ± 1.21 kJ/mol by drop solution calorimetry in molten sodium molybdate (3Na 2 O·MoO 3 ) at 975 K. The corresponding heat of formation from oxides at 298 K was −261.12 ± 3.02 kJ/mol. This ternary glass is shown to be slightly metastable with respect to binary crystalline components (K 2 CO 3 and MgCO 3 ) and may be further stabilized by entropy terms arising from cation disorder and carbonate group distortions. This high degree of disorder is confirmed by 13 C MAS NMR measurement of the average chemical shift tensor values, which show asymmetry of the carbonate anion to be significantly larger than previously reported values. Molecular dynamics simulations show that the structure of this carbonate glass reflects the strong interaction between the oxygen atoms in distorted carbonate anions and potassium cations.

Aluminum (Al) oxides are important adsorbents for phosphate in soils and sediments, and significantly limit Phosphate (P) mobility and bioavailability, but the speciation of surface-adsorbed phosphate on Al oxides remains poorly understood. Here, phosphate sorption speciation on amorphous Al hydroxide (AAH) was determined under pH 3–8 and P concentration of 0.03 mM–15 mM using various spectroscopic approaches, and phosphate precipitation mechanisms were discussed as well. AAH exhibits an extremely high phosphate sorption capacity, increasing from 3.80 mmol/g at pH 7 to 4.63 mmol/g at pH 3. Regardless of reaction pH, with increasing P sorption loading, the sorption mechanism transits from bidentate binuclear (BB) surface complexation with dP-Al of 3.12 Å to surface precipitation of analogous amorphous AlPO4 (AAP), possibly with ternary complexes, such as (≡Al-O)2-PO2-Al, as intermediate products. Additionally, the percentage of precipitated phosphate occurring in AAP linearly and positively correlates with P sorption loading. Compared to phosphate reaction with ferrihydrite, phosphate adsorbs and precipitates more readily on AAH due to the higher solubility product (Ksp) of AAH. The formation of AAP particles involves AlIII release, which is promoted by phosphate adsorption, and its subsequent precipitation with phosphate at AAH surfaces or in the bulk solution.

The formation of ordered polydiacetylenes (PDAs) from conjugated triynes and longer polyynes has proven challenging due to the low stability of the starting materials and the possibility of varying regiochemistry for the polymerization. We report here the preparation of host-guest cocrystals of diiodohexatriyne and diiodooctatetrayne, each with a bis(nitrile)oxalamide host. Single-crystal X-ray diffraction studies show that the halogen-bonding interactions between the host and guest align the diiodopolyyne monomers with the proper parameters for 1,4-topochemical polymerization. Using Raman spectroscopy, solid-state C-13 MAS NMR, and single-crystal X-ray diffraction, we have demonstrated the formation of a single highly ordered PDA, poly(iodoethynyliododiacetylene) (PIEDA), from the 1,4-polymerization of diiodohexatriyne. Diiodooctatetrayne also forms ordered cocrystals, but attempts to form polymer from these crystals led to disordered species. This work represents the first reported single-crystal-to-single-crystal 1,4-polymerization of a conjugated triyne.

Hydroxyapatite (Hap) has been shown to be an excellent sorbent for F- removal of elevated levels of fluoride in groundwater worldwide; however, the molecular mechanisms of this process have not been clearly addressed. Herein, we used F-19 solid-state NMR spectroscopy to investigate F- sorption mechanisms by nanosized Hap combined with H-1 NMR and H-1{F-19}) Rotational Echo DOble Resonance (REDOR) technology in addition to other characterization methods such as Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD) and Nanoscale Secondary Ion Mass Spectroscopy (NanoSIMS). Our experimental results showed that F- sorption mechanisms depend on solution pH and fluoride concentration ([F-]). At pH 7 and [F-] <= 50 mM, a single 19F NMR peak at -103 ppm was observed, which could be assigned to fluorapatite [ca(5)(PO4)(3)F] (Fap) or fluoro-hydroxyapatite solid solution [Ca-5(PO4)(3)F-x(OH)(1-x); x = 0-1] (F-Hap). A simultaneous formation of fluorite (CaF2) precipitates (delta(F-19) = -108 ppm) was observed at higher [r] (e.g., 100 mM), which was further confirmed by TEM and XRD analysis. The NanoSIMS and H-1{F-19) REDOR analyses indicated that a dissolution-precipitation process was involved in the F- sorption on Hap. Our results strongly support the efficacy of Hap for F- removal even after several instances of regeneration, making it a cost-effective strategy for fluoride treatment. (C) 2019 Elsevier Inc. All rights reserved.

Carbonate glasses can be formed routinely in the system K2CO3–MgCO3. The enthalpy of formation for one such 0.55K2CO3–0.45MgCO3 glass was determined at 298 K to be 115.00 ± 1.21 kJ/mol by drop solution calorimetry in molten sodium molybdate (3Na2O·MoO3) at 975 K. The corresponding heat of formation from oxides at 298 K was −261.12 ± 3.02 kJ/mol. This ternary glass is shown to be slightly metastable with respect to binary crystalline components (K2CO3 and MgCO3) and may be further stabilized by entropy terms arising from cation disorder and carbonate group distortions. This high degree of disorder is confirmed by 13C MAS NMR measurement of the average chemical shift tensor values, which show asymmetry of the carbonate anion to be significantly larger than previously reported values. Molecular dynamics simulations show that the structure of this carbonate glass reflects the strong interaction between the oxygen atoms in distorted carbonate anions and potassium cations.

Bobdownsite, IMA number 2008-037, was approved as a new mineral by the Commission on New Minerals, Nomenclature and Classification (CNMNC) as the fluorine end-member of the mineral whitlockite. The type locality of bobdownsite is in Big Fish River, Yukon, Canada, and bobdownsite was reported to be the first mineral with essential monofluorophosphate (PO3F2-). The type specimen of bobdownsite has been reinvestigated by electron probe microanalysis (EPMA), and our data indicate that fluorine abundances are below detection in the mineral. In addition, we conducted detailed analysis of bobdownsite from the type locality by gas chromatography isotope ratio mass spectrometry, Raman spectroscopy, EPMA, and NMR spectroscopy. These data were compared with previously published data on synthetic monofluorophosphate salts. Collectively, these data indicate that bobdownsite is indistinguishable from whitlockite with a composition along the whitlockite-merrillite solid solution. Bobdownsite is therefore discredited as a valid mineral species. An additional mineral, krasnoite, has been purported to have monofluorophosphate components in its structure, but reexamination of those data indicate that F-in krasnoite forms bonds with Al, similar to OH-bonded to Al in perhamite. Consequently, krasnoite also lacks monofluorophosphate groups, and there are currently no valid mineral species with monofluorophosphate in their structure. We recommend that any future reports of new minerals that contain essential monofluorophosphate anions be vetted by abundance measurements of fluorine, vibrational spectroscopy (both Raman and FTIR), and where paramagnetic components are permissibly low, NMR spectroscopy. Furthermore, we emphasize the importance of using synthetic compounds containing monofluorophosphate anions as a point of comparison in the identification of minerals with essential monofluorophosphate. Structural data that yield satisfactory P-F bond lengths determined by X-ray crystallography, coupled with direct chemical analyses of fluorine in a material do not constitute sufficient evidence alone to identify a new mineral with essential monofluorophosphate.

8 1 NASA Johnson Space Center, Mailcode XI2, 2101 NASA Parkway, Houston, TX 77058, USA 9 2 Institute of Meteoritics, MSC03 2050, University of New Mexico, 200 Yale Blvd SE, 10 Albuquerque, NM 87131, USA 11 3 Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100, USA 12 4 Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, NV, 89154, USA 13 5 Department of Natural History, Royal Ontario Museum, 100 Queen’s Park, Toronto, Ontario 14 M5S 2C6, Canada 15 6 Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd., N.W, 16 Washington, DC 20015, USA 17 7 Department of Earth and Planetary Sciences, University of New Mexico, 200 Yale Blvd SE, 18 Albuquerque, NM 87131, USA 19 8 Jacobs Technology, NASA Johnson Space Center, Mailcode XI, 2101 NASA Parkway, 20 Houston, TX 77058, USA 21

A polycrystalline specimen of liebermannite [KAlSi3O8 hollandite] was synthesized at 14.5GPa and 1473 K using glass starting material in a uniaxial split-sphere apparatus. The recovered specimen is pure tetragonal hollandite [SG: I4/m] with bulk density of within 98% of the measured X-ray value. The specimen was also characterized by Raman spectroscopy and nuclear magnetic resonance spectroscopy. Sound velocities in this specimen were measured by ultrasonic interferometry to 13GPa at room T in a uniaxial split-cylinder apparatus using Al2O3 as a pressure marker. Finite strain analysis of the ultrasonic data yielded KS0=145(1)GPa, K0′=4.9(2), G0=92.3(3)GPa, G0′=1.6(1) for the bulk and shear moduli and their pressure derivatives, corresponding to VP0=8.4(1)km/s,VS0=4.9(1)km/s for the sound wave velocities at room temperature. These elasticity data are compared to literature values obtained from static compression experiments and theoretical density functional calculations.

A series of synthetic F,Cl apatites with low hydroxyl content was investigated using P-31, F-19, and Cl-35 solid-state magic angle spinning (MAS) NMR spectroscopic methods. P-31 single-pulse (SP) NMR spectra show that for each composition the phosphate P-31 chemical shift depends on occupancy of the nearest anion site for each composition. Overall the average chemical shift deviates from linear across the F/Cl series. For intermediate compositions F-19 SP NMR spectra reveal complex, broadened spectral profiles that are not correlated to composition. F-19{Cl-35} TRAPDOR results indicate that the spectral profiles do not reflect occupancy of F and Cl in adjacent column anion sites. We propose that the complex F-19 lineshapes are principally due to broad distributions of F-19 Ca distances arising from displacement of F along the anion channel. Approximate fluorine atomic positions are estimated based on F-19 chemical shifts of alkaline earth fluoride salts, and the results are in good accord with those proposed for intermediate composition F,Cl apatites from XRD data.