Minerals Forsterite Research Articles

The Hugoniot curve and sound velocity of forsterite to 1200 GPa

The comprehension of the composition and physical state of the deep interiors of large planets, as well as the impact events pertinent to planetary formation and evolution, necessitates an understanding of the properties of planetary materials under extreme conditions. Forsterite (Mg2SiO4), a significant geological mineral, has not been fully characterized in terms of its behavior under shock compression due to a lack of consensus among previous experiments and simulations aimed at determining its Hugoniot, as well as the absence of knowledge of sound velocity at high pressures, a critical parameter indicative of phase transformation and melting.In this study, we delineated the Hugoniot curve of the mineral forsterite up to immense pressures of 1200 GPa. For the first time, we successfully constrained its sound velocity along the Hugoniot curve up to 760 GPa by combining laser-driven shock experiments with first-principles molecular dynamics simulations. The measured Hugoniot data for forsterite corroborated previous findings and suggested the occurrence of incongruent melting during shock compression. Remarkably, along their respective Hugoniot curves, the sound velocity of forsterite was observed to fall between that of the minerals bridgmanite and periclase. The remarkable agreement between the experimental results and simulation data provides reliable sound velocity measurements on the forsterite Hugoniot, which is critical for comprehensively understanding the phase transition and melting behavior of forsterite under ultra-high pressures. This knowledge sheds invaluable light on the behavior of this significant geological mineral under extreme conditions akin to those found in the interiors of planets.

Adsorption of HCN on cosmic silicates: a periodic quantum mechanical study.

Hydrogen cyanide (HCN) represents a small but widely distributed fraction of the interstellar molecules, and it has been observed in all the environments characterizing the formation of a new planetary system. HCN can polymerize to form biomolecules, including adenine (H5C5N5), and it has drawn attention as a possible precursor of several building blocks of life due to the presence of its polymerization products in meteorites, comets and other asteroidal bodies. To elucidate the potential catalytic role that cosmic silicates have played in these processes, we have investigated, at DFT-PBE level inclusive of a posteriori dispersion correction, the energetic and spectroscopic features of the adsorption of HCN molecules on the most relevant crystalline surfaces of the mineral forsterite (Mg2SiO4), a common silicate constituent of the interstellar core grains and planetary rocky bodies. The results reveal that HCN adsorbs both in molecular and dissociative ways, within a wide range of adsorption energies (-29.4 to -466.4 kJ mol-1). Thermodynamic and kinetic results show that dissociative adsorption is dominant already at low temperatures, a fact particularly relevant at the protoplanetary conditions (i.e., the latest stages in the star system formation process). The simulated spectroscopic features of the studied adducts show a wide range of different degrees of perturbation of C-H and CN bonds. This finding agrees with previous experimental works, and our results confirm that a complex chemistry is observed when this astrochemically-relevant molecule interacts with Mg2SiO4, which may be associated with a considerable potential reactivity towards the formation of relevant prebiotic compounds.

Nanoscale Mg-Depleted Layers Slow Carbonation of Forsterite (Mg2SiO4) When Water Is Limited

Passivation of silicate surfaces by accumulated reaction products is an obstacle to efficient CO2 mineralization. In this study, we investigate a unique passivation effect during the carbonation of the basalt mineral forsterite (Mg2SiO4) in humid supercritical CO2 (50 °C, 90 bar). Using in situ high-pressure infrared spectroscopy, we demonstrate that dissolution of forsterite into a thin water film slows significantly after reaction for ≈24 h, even under far-from-equilibrium conditions. 29Si magic angle spinning nuclear magnetic resonance spectroscopy detects a highly polymerized amorphous silica at this stage. On the basis of transmission electron microscopy and energy dispersive X-ray spectroscopy, we show that the silica is present as a Mg-depleted layer that is just 2–3 nm thick on the reacted forsterite particles. The decrease in the level of forsterite dissolution in the presence of an extraordinarily thin Mg-depleted layer can be strongly linked to properties of the thin fluid film at the surface, highlighting the importance of water during mineral carbonation. This study furthers our understanding of silicate mineral carbonation under select low-water, humidified fluid conditions relevant to basaltic geologic reservoirs, recovery of critical elements by carbonation of mafic ores, and sequestration of atmospheric CO2 by enhanced rock weathering.

Synthesis of mesoporous silica using a mineral silica source

AbstractMesoporous silica has been applied in catalysis, separations, and drug delivery. It has generally been made using organosilicon precursors such as tetraethyl orthosilicate. For sustainability, it is necessary to find readily accessible mineral sources for making mesoporous silica. In this work, we demonstrate the successful synthesis of mesoporous silica with 10 nm average pore size using the mineral forsterite (Mg2SiO4) as a silica source, providing a potentially cheaper and more Earth‐friendly route to making technologically important porous silica materials. Pure forsterite was synthesized by a solid‐state chemistry route at 1000°C and underwent dissolution–reprecipitation in aqueous hydrochloric acid containing the soft template surfactant, Pluronic P123. Variations of initial reaction pH (−0.2 to 0.6), reaction time (12–24 h), reaction temperature (50 to 90°C), and silica precursor (forsterite and fumed silica) were performed. The mesoporous silica aged at 70°C for 24 h had the highest porosity, with a surface area of 735 m2/g and a pore volume of 1.4 ml/g, comparable to mesoporous silica made using conventional starting materials. This novel geomimetic synthesis route supports the possibility of analogous formation of structured (mesoporous or zeolitic) silica in nature under abiotic or prebiotic conditions.

Silicate Melting and Vaporization During Rocky Planet Formation

AbstractCollisions that induce melting and vaporization can have a substantial effect on the thermal and geochemical evolution of planets. However, the thermodynamics of major minerals are not well known at the extreme conditions attained during planet formation. We obtained new data at the Sandia Z Machine and use published thermodynamic data for the major mineral forsterite (Mg SiO ) to calculate the specific entropy in the liquid region of the principal Hugoniot. We use our calculated specific entropy of shocked forsterite, and revised entropies for shocked silica, to determine the critical impact velocities for melting or vaporization upon decompression from the shocked state to 1 bar and the triple points, which are near the pressures of the solar nebula. We also demonstrate the importance of the initial temperature on the criteria for vaporization. Applying these results to ‐body simulations of terrestrial planet formation, we find that up to 20% to 40% of the total system mass is processed through collisions with velocities that exceed the criteria for incipient vaporization at the triple point. Vaporizing collisions between small bodies are an important component of terrestrial planet formation.

Impacts of diffusive transport on carbonate mineral formation from magnesium silicate-CO2-water reactions.

Reactions of CO2 with magnesium silicate minerals to precipitate magnesium carbonates can result in stable carbon sequestration. This process can be employed in ex situ reactors or during geologic carbon sequestration in magnesium-rich formations. The reaction of aqueous CO2 with the magnesium silicate mineral forsterite was studied in systems with transport controlled by diffusion. The approach integrated bench-scale experiments, an in situ spectroscopic technique, and reactive transport modeling. Experiments were performed using a tube packed with forsterite and open at one end to a CO2-rich solution. The location and amounts of carbonate minerals that formed were determined by postexperiment characterization of the solids. Complementing this ex situ characterization, (13)C NMR spectroscopy tracked the inorganic carbon transport and speciation in situ. The data were compared with the output of reactive transport simulations that accounted for diffusive transport processes, aqueous speciation, and the forsterite dissolution rate. All three approaches found that the onset of magnesium carbonate precipitation was spatially localized about 1 cm from the opening of the forsterite bed. Magnesite was the dominant reaction product. Geochemical gradients that developed in the diffusion-limited zones led to locally supersaturated conditions at specific locations even while the volume-averaged properties of the system remained undersaturated.

Nitrogen solubility in upper mantle minerals

Nitrogen solubility in the upper mantle minerals forsterite, diopside, enstatite and pyrope has been quantified by SIMS measurements of nitrogen-saturated, synthetic samples. The crystals were grown in a 15N–H–O fluid buffered by Ni–NiO, Co–CoO, and Fe–FeO, at 1000–1300 °C and 15–35 kbar in a piston cylinder apparatus. Nitrogen solubility in minerals is significantly affected by temperature, pressure, mineral composition and, in particular, by oxygen fugacity. Nitrogen in all crystals buffered by Ni–NiO or Co–CoO is below detection limit or at most a few μg/g at very high pressures. Concentrations of 5–24 μg/g nitrogen have been quantified in diopside, enstatite and pyrope buffered by Fe–FeO at 1100 °C/15 kbar. Very high nitrogen solubility up to 100 μg/g is observed at the Fe–FeO buffer in enstatite at high-temperature or in Al-bearing enstatite and diopside. The nitrogen solubility in forsterite at the Fe–FeO buffer also clearly increases with temperature and pressure; a maximum solubility of 10 ppm is obtained at 1300 °C/35 kbar. The strong enhancement of nitrogen solubility under reducing conditions may be related to nitrogen dissolution as either NH+4 or as N3− directly replacing O2−. Both mechanisms require some charge compensation, consistent with the enhancement of nitrogen solubility with Al content in enstatite. Our results demonstrate that the reduced lower part of the upper mantle has a large nitrogen storage capacity, and may store ∼20–50 times more nitrogen than the present atmosphere. Therefore, some ‘missing’ nitrogen may still be retained in the Earthʼs deep, reduced mantle. The calculated nitrogen partition coefficients between upper mantle minerals and silicate melt reveal that an oxidized mantle source would lose almost its entire nitrogen during partial melting, whereas under reducing conditions a considerable fraction of nitrogen could be retained in the residual solids. The high nitrogen solubility in upper mantle minerals at reducing conditions also suggests that solidification of the magma ocean on the early Earth should have retained significant nitrogen, yielding higher N/Ar and N/C ratios in the young upper mantle as compared to the young atmosphere.

Silicate Carbonation in Supercritical CO2 Containing Dissolved H2O: An in situ High Pressure X-Ray Diffraction and Infrared Spectroscopy Study

Technological advances have been significant in recent years for managing environmentally harmful emissions (mostly CO2) resulting from combustion of fossil fuels. Deep underground geologic formations are viewed as reasonable options for long-term storage of CO2, but mechanisms controlling the stability of rocks and minerals in contact with injected supercritical fluids containing water are relatively unknown. In this paper, we discuss mineral transformation reactions occurring between supercritical CO2 containing water and the silicate minerals forsterite (Mg2SiO4), wollastonite (CaSiO3), and enstatite (MgSiO3). We utilized newly developed in situ high pressure x-ray diffraction (HXRD) and in situ infrared (IR) spectroscopic capabilities to examine the mineral transformation reactions. Forsterite and enstatite were selected as they are important minerals present in igneous and mafic rocks. Wollastonite, classified as a pyroxenoid (similar to a pyroxene), was chosen as a suitably fast-reacting proxy for examining silicate carbonation processes. The experiments were conducted under modest pressures (90 to 160bar), temperatures between 35° to 70° C, and varying concentrations of water dissolved in the scCO2. Under these conditions, scCO2 contains up to 3,500ppm dissolved water. Forsterite carbonation products identified by in situ HXRD included nesquehonite and magnesite. Wollastonite produced calcite and no detectable crystalline hydrated carbonates. In contrast, enstatite was the least reactive, based on in situ HXRD data that contained no detectable crystalline carbonation. Based on in situ IR spectroscopic measurements, mineral surface hydration processes are critical for these reactions. Thicker water films were associated with forsterite and wollastonite compared to enstatite. Carbonation was evidenced by the appearance and growth of asymmetric C-O stretching bands of carbonate precipitates (1400 to 1550 cm-1), and carbonation extents were correlated to water-film thicknesses. Overall, these fundamental studies are beginning to illustrate processes controlling carbonation rates and potentials of silicate minerals.

Optimized conditions for imaging the effects of bonding charge density in electron microscopy

We report on the observability of valence bonding effects in aberration-corrected high resolution electron microscopy (HREM) images along the [010] projection of the mineral Forsterite (Mg₂SiO₄). We have also performed exit wave restorations using simulated noisy images and have determined that both the intensities of individual images and the modulus of the restored complex exit wave are most sensitive to bonding effects at a level of 25% for moderately thick samples of 20-25 nm. This relatively large thickness is due to dynamical amplification of bonding contrast arising from partial de-channeling of 1s states. Simulations also suggest that bonding contrast is similarly high for an un-corrected conventional electron microscope, implying an experimental limitation of signal to noise ratio rather than spatial resolution.

Metal Carbonation of Forsterite in Supercritical CO2 and H2O Using Solid State 29Si, 13C NMR Spectroscopy

Ex situ solid state NMR was used for the first time to study fundamental mineral carbonation processes and reaction extent relevant to geologic carbon sequestration (GCS) using a model silicate mineral forsterite (Mg2SiO4)+supercriticalCO2 with and without H2O. Run conditions were 80 C and 96 atm. 29Si NMR clearly shows that in the absence of CO2, the role of H2O is to hydrolyze surface Mg-O-Si bonds to produce dissolved Mg2+, and mono- and oligomeric hydroxylated silica species. Surface hydrolysis products contain only Q0 (Si(OH)4) and Q1(Si(OH)3OSi) species. An equilibrium between Q0, Q1 and Mg2+ with a saturated concentration equivalent to less than 3.2% of the Mg2SiO4 conversion is obtained at a reaction time of up to 7 days. Using scCO2 without H2O, no reaction is observed within 7 days. Using both scCO2 and H2O, the surface reaction products for silica are mainly Q3 (SiOH(OSi)3) species accompanied by a lesser amount of Q2 (Si(OH)2(OSi)2) and Q4 (Si(OSi)4). However, no Q0 and Q1 were detected, indicating the carbonic acid formation/deprotonation and magnesite (MgCO3) precipitation reactions are faster than the forsterite hydrolysis process. Thus it can be concluded that the Mg2SiO4 hydrolysis process is the rate limiting step of the overall mineral carbonation process.more » 29Si NMR combined with XRD, TEM, SAED and EDX further reveal that the reaction is a surface reaction with the Mg2SiO4 crystallite in the core and with condensed Q2-Q4 species forming amorphous surface layers. 13C MAS NMR identified a possible reaction intermediate as (MgCO3)4-Mg(OH)2-5H2O. However, at long reaction times only crystallite magnesite MgCO3 products are observed.« less

Boron Removal via Formation of Magnesium Silicate Solids during Precipitative Softening

Precipitative softening is an option to remove silicon and boron from natural waters. Silicon was removed from hard waters by precipitative softening when the molar ratio of Mg:Si was less than 6:1 by the formation of an amorphous magnesium silicate. This solid had an apparent solubility product constant of 10 -25.66 and was stoichiometrically similar to the mineral forsterite, Mg 2 SiO 4 . Boron removal was consistent with sorption to this amorphous magnesium silicate and could be roughly described by a Freundlich isotherm: B sorb /Mg 2 SiO 4(s) =21×B 0.51 sol .

Recipes for making synthetic CAIs, refractory residues, and minerals for rim-forming experiments

Abstract— Recipes are presented for synthesizing various type A and type B Ca-Al-rich inclusions (CAIs), refractory volatilization residues, and the minerals forsterite and melilite that are required for experiments. These experiments (described in other works) aim to make two determinations: 1) the conditions under which the surfaces of CAIs were either “flash-heated” or “volatilized subsolidus” to form a temporary ultra-refractory residue, and 2) the conditions under which the residue was then metasomatized to form the mineral layers making up Wark-Lovering (WL) rims on CAIs.

Hydrogen defects in Forsterite: A test case for the embedded cluster method

We present a theoretical study of several hydrogen defects in the upper mantle mineral forsterite using a quantum mechanical embedded cluster approach. We make extensive comparisons with results obtained using Mott–Littleton calculations and data from periodic density functional studies by ourselves and other authors. We show that the embedded cluster method gives reliable energies for a range of defect reactions, including cation vacancy formation, binding between defects, and formation of hydrogen defects by reaction with water. We propose that the embedded cluster techniques should be the method of choice when studying point defects in minerals.

Partitioning of Actinides, Rare Earth Elements, and Other Trace Elements In Titanium-Rich Veins From Adamello, Italy

ABSTRACTExtensive mineralogical and chemical studies have been carried out on the Ti-rich hydrothermal veins emplaced within the contact aureole of the Adamello batholith. In addition to other actinide and rare earth element host phases, the veins contain both zirconolite and betafite and provide information relevant to ceramic wasteforms designed for the disposal of actinide-rich nuclear wastes. In this paper, we describe the results of element partitioning studies based on dissolution experiments using 9M HCl. Generally, the acid-resistant minerals include allanite, baddeleyite, betafite, chalcopyrite, geikielite, titanite, spinel, and zirconolite. We also found that the major silicate minerals forsterite, phlogopite, and titanian clinohumite and the sulfide mineral pyrrhotite are partially dissolved by the acid treatment, whereas calcite and apatite are highly soluble (as expected). In particular, the distributions of Th and U between the acid-resistant and acid-soluble fractions indicate that they partition mainly between zirconolite, titanite, betafite, and apatite. However, there is a considerable increase in the amounts of Zr, Nb, Th, and U released in certain actinide-rich samples that may result from enhanced dissolution following radiation damage.

Gel synthesis of magnesium silicates: A 29Si magic angle spinning NMR study

The formation of the magnesium silicate minerals forsterite, enstatite, and roedderite by heating of amorphous “protosilicate” gels precipitated from aqueous solution has been studied by 29Si MAS nmr. Gentle drying of the hydrogels at 110° C gives materials with broad nmr signals that do not differ appreciably with preparation conditions, but the minerals formed by heating at 750° C or higher are greatly dependent on the precipitation and washing conditions of the original gel. The rare mineral roedderite, best known from studies of unequilibrated enstatite chondrite meteorites, becomes a major species along with forsterite when the hydrogels are washed with sodium hydroxide solution before drying and heating to 750° C.

Phonon Density of States and Specific Heat of Forsterite, Mg 2 SiO 4

The phonon density of states of the geophysically important mineral forsterite has been calculated with a rigid-ion model, which gives good agreement with an experimental measurement by inelastic neutron scattering. The density of states has been used to calculate the specific heat as a function of temperature, the results of which are in excellent agreement with calorimetrically measured values. The rigid-ion model takes account of the interatomic interactions and normal modes of vibration on a detailed microscopic basis, and is therefore more realistic than the Debye and other empirical models used previously.

Carbonation of peridotites and decarbonation of siliceous dolomites represented in the system CaO-MgO-SiO 2-CO 2 to 30 kbar

The decarbonation of siliceous dolomite produces rocks including the minerals forsterite, orthopyroxene and clinopyroxene, characteristic of peridotites. Selected reactions in the system CaO-MgO-SiO2 -CO2 are reviewed and published data at crustal and mantle pressures are compared with previously unpublished experimental results between 15 and 30 kbar for five reactions: (0) magnesite + clinopyroxene = dolomite + orthopyroxene; (1) magnesite + quartz = enstatite + CO 2; (5) dolomite + orthopyroxene + quartz = clinopyroxene + CO 2; (3) magnesite + enstatite = forsterite + CO 2; (6) dolomite + orthopyroxene = clinopyroxene + forsterite+ CO 2. Reactions (0), (1) and (5) meet at an invariant point near 1090°C and 34 kbar. Reactions (3) and (6) represent the carbonation of model harzburgite and Iherzolite, respectively. Dolomites in reaction (6) contain more than 70 wt.% CaCO 3, at temperatures below the crest of the calcite-dolomite solvus, they are magnesian calcites. Phase relationships for carbonated model peridotites in the presence of H 2O, compared with estimated depths and temperatures of equilibration of xenoliths from the Premier Mine kimberlite, indicate that within limited depth intervals solid magnesite-harzburgite can coexist with partially melted lherzolite. Eruption of kimberlite could transport xenoliths of Iherzolite and magnesite-harzburgite. Experiments indicate that the magnesite dissociates within minutes during uprise. This observation is consistent with the proposal of Boyd and Gurney that low-calcium garnets in kimberlites of the Kaapvaal-Rhodesian craton are produced by disruption of magnesite disseminated through depleted harzburgites in the roots of the craton, within the diamond stability field.