Volume 101, Issue 9

Many igneous rocks contain mineral assemblages that are not appropriate for application of common mineral equilibria or oxybarometers to estimate oxygen fugacity. Spinel-structured oxides, common minerals in many igneous rocks, typically contain sufficient V for XANES measurements, allowing use of the correlation between oxygen fugacity and V K pre-edge peak intensity. Here we report V pre-edge peak intensities for a wide range of spinels from source rocks ranging from terrestrial basalt to achondrites to oxidized chondrites. The XANES measurements are used to calculate oxygen fugacity from experimentally produced spinels of known fo2${f_{{{\rm{o}}_2}}}$. We obtain values, in order of increasing fo2${f_{{{\rm{o}}_2}}}$, from IW-3 for lodranites and acapulcoites, to diogenites, brachinites (near IW), ALH 84001, terrestrial basalt, hornblende-bearing R chondrite LAP 04840 (IW+1.6), and finally ranging up to IW+3.1 for CK chondrites (where the ΔIW logfo2$\log {f_{{{\rm{o}}_2}}}$ of a sample relative to the logfo2$\log {f_{{{\rm{o}}_2}}}$ of the IW buffer at specific T). To place the significance of these new measurements into context we then review the range of oxygen fugacities recorded in major achondrite groups, chondritic and primitive materials, and planetary materials. This range extends from IW-8 to IW+2. Several chondrite groups associated with aqueous alteration exhibit values that are slightly higher than this range, suggesting that water and oxidation may be linked. The range in planetary materials is even wider than that defined by meteorite groups. Earth and Mars exhibit values higher than IW+2, due to a critical role played by pressure. Pressure allows dissolution of volatiles into magmas, which can later cause oxidation or reduction during fractionation, cooling, and degassing. Fluid mobility, either in the sub-arc mantle and crust, or in regions of metasomatism, can generate values >IW+2, again suggesting an important link between water and oxidation. At the very least, Earth exhibits a higher range of oxidation than other planets and astromaterials due to the presence of an O-rich atmosphere, liquid water, and hydrated interior. New analytical techniques and sample suites will revolutionize our understanding of oxygen fugacity variation in the inner solar system, and the origin of our solar system in general.

The preservation of bone or bioapatite over geologic time has presented paleobiologists with long-standing and formidable questions. Namely, to elucidate the mechanisms, processes, rates, and depositional conditions responsible for the formation of a fossil from a once living tissue. Approaches integrating geochemistry, mineralogy, physics, hydrology, sedimentology, and taphonomy have all furthered insights into fossilization, but several fundamental gaps still remain. Notably, our limited understanding of: (1) the timing of processes during diagenesis (e.g., early and/or late), (2) the rate of bioapatite transformation into thermodynamically more stable phases, (3) the controls imparted by depositional environment, and (4) the role of (micro)biology in determining the fate of bone bioapatite (dissolution or preservation). The versatility of fossil bioapatite to provide information on the biology of extinct vertebrates rests on our ability to identify and characterize the changes that occurred to bioapatite during diagenesis. This review will evaluate our current understanding of bioapatite diagenesis and fossilization, focusing on the biogeochemical transformations that occur during diagenesis to the mineral and organic components of bone (excluding teeth and enamel), the analytical approaches applied to evaluate fossilization processes, and outline some suggestions for future promising directions.

Olivine is distinguished from all other minerals in providing a remarkable chemical narrative about magmatic processes that occurred in Earth’s crust, mantle, and core over the entire age of Earth history. Olivines in mantle peridotite have Ni contents and Mg numbers that were largely produced by equilibrium crystallization in an early turbulently convecting magma ocean; subsequent stages of partial melting operated to slightly elevate Ni and Mg number in residual olivines. Olivines from Archean komatiites from the Abitibi greenstone belt have Ni contents and Mg numbers that are consistent with an extensively melted peridotite source at great depths in the mantle. Olivines from basaltic oceanic crust, the Icelandic mantle plume and other Phanerozoic occurrences have compositions that record magma chamber crystallization, recharge, mixing, and partial melting. Olivines from the present-day Icelandic mantle plume have compositions that are consistent the melting of a peridotite source; unlike Hawaii, the melting of recycled crust as a distinct pyroxenite lithology is not evident in the olivine chemistry of Iceland. Paleocene picrites from Baffin Island and West Greenland from the ancient Icelandic plume have olivines with Ni contents that are consistent with either Ni-rich peridotite that formed by core-mantle interaction or by low-pressure crystallization of hot and deep magmas. In general, hot magma oceans, mantle plumes, and ambient mantle magmatism form in ways that are captured by the compositions of the olivine crystals that they contain.

The ascent of H 2 O- and H 2 O-CO 2 -bearing basaltic melts from the deeper to the shallower part of the Stromboli magmatic system and their vesiculation were simulated from decompression experiments. A well-studied “golden” pumice produced during an intermediate- to a large-scale paroxysm was used as starting material. Volatile-bearing glasses were synthesized at an oxygen fugacity fo2${f_{{{\rm{o}}_2}}}$ ranging from NNO-1.4 to +0.9, 1200 °C and 200 MPa. The resulting crystal- and bubble-free glasses were then isothermally (1200 °C) decompressed to final pressures P f ranging between 200 and 25 MPa, at a linear ascent rate of 1.5 m/s (or 39 kPa/s) prior to be rapidly quenched. Textures of post-decompression glasses that were characterized by X-ray computed tomography result from different mechanisms of degassing that include bubble nucleation, growth, coalescence, and outgassing, as well as fragmentation. Homogeneous bubble nucleation occurs for supersaturation pressures (difference between saturation pressure and pressure at which bubbles start to form homogeneously, Δ P HoN ) ≤ 50 MPa. In the CO 2 -free melts, homogeneous nucleation occurs as two distinct events, the first at high P f (200–150 MPa) and the second at low P f (50–25 MPa) near the fragmentation level. In contrast, in the CO 2 -bearing melts, multiple events of homogeneous bubble nucleation occur over a substantial P f interval along the decompression path. Bubble coalescence occurs in both H 2 O- and H 2 O-CO 2 -bearing melts and is the more strongly marked between 100 and 50 MPa P f . The CO 2 -free melts follow equilibrium degassing until 100 MPa P f and are slightly supersaturated at 60 and 50 MPa P f , thus providing the driving force for the second bubble nucleation event. In comparison, disequilibrium degassing occurs systematically in the CO 2 -bearing melts that retain high CO 2 concentrations. Fragmentation was observed in some CO2-free charges decompressed to 25 MPa P f and is intimately associated with the occurrence of the second bubble nucleation event. Textures of H 2 O-CO 2 -bearing glasses reproduce certain critical aspects of the Stromboli natural textures (bubble number densities, shapes, sizes, and distributions) and chemistries (residual volatile concentrations). Average bubble sizes, bubble size distribution (BSD), and bubble number density (BND) data are used together to estimate that the “golden” pumice magmas ascend from their source region in 43 to 128 min.

Nanophase Fe-oxyhydroxides in freshwater ferromanganese nodules (FFN) from Green Bay, Lake Michigan, and adsorbed arsenate have been investigated by X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Z-contrast imaging, and ab initio calculations using the density functional theory (DFT). The samples from northern Green Bay can be divided into two types: Fe-Mn nodules and Fe-rich nodules. The manganese-bearing phases are todorokite, birnessite, and buserite. The iron-bearing phases are feroxyhyte, nanophase goethite, two-line ferrihydrite, and nanophase FeOOH with guyanaite structure. Z-contrast images of the Fe-oxyhydroxides show ordered FeOOH nano-domains with guyanaite structure intergrown with nanophase goethite. The FeOOH nanophase is a precursor to the goethite. Henceforth, we will refer to it as “proto-goethite.” DFT calculations indicate that goethite is more stable than proto-goethite. Our results suggest that ordering between Fe and vacancies in octahedral sites result in the transformation from feroxyhyte to goethite through a proto-goethite intermediate phase. Combining Z-contrast images and TEM-EDS reveals that arsenate (AsO43−${\rm{AsO}}_4^{3 - }$) tetrahedra are preferentially adsorbed on the proto-goethite (001) surface via tridentate adsorption. Our study directly shows the atomic positions of Fe-oxyhydroxides with associated trace elements. The methods can be applied for identifying structures of nano-phases and adsorbed trace elements and heavy metals.

It is well accepted that the Earth formed by the accretion and collision of small (10–100 km), rocky bodies called planetesimals. W-Hf isotopic evidence from meteorites suggest that the cores of many planetesimals formed within a relatively short time frame of ~3 My. While a very hot, deep magma ocean is generally thought to have been the driving mechanism for core formation in large planetary bodies, it inadequately explains differentiation and core formation in small planetesimals due to temperatures potentially being insufficient for wide-scale silicate melting to occur. In order for these planetesimals to differentiate within such a relatively short time without a magma ocean, a critical melt volume of the metallic (core-forming) phase and sufficient melt connectivity and grain size must have existed to attain the required permeability and lead to efficient core formation. Shear deformation may increase the connectedness of melt and the permeability, and thus could have been a major contributing factor in the formation of planetesimal cores. This deformation may have been caused by large impacts and collisions experienced by the planetesimals in the early solar system. The purpose of this work is to test the hypothesis that shear deformation enhances the connectivity and permeability of Fe-S melt within a solid silicate (olivine) matrix, such that rapid core formation is plausible. A rotational Drickamer apparatus (RDA) was used to heat and torsionally deform a sample of solid olivine + FeS liquid through six steps of large-strain shear deformation. After each deformation step, X-ray microtomographs were collected in the RDA to obtain in situ three-dimensional images of the sample. The resulting digital volumes were processed and permeability simulations utilizing the lattice Boltzmann method were performed to determine the effect of shear deformation on connectivity and permeability within the sample. The resulting permeabilities of the sample at various steps of deformation are the same within uncertainty and do not exhibit a change with increasing deformation. Additionally, the migration velocity calculated from the permeability of the sample is not high enough for segregation to take place within the time frame of ~3 My. In addition to further constraining the mechanism of core formation in planetesimals, the image processing techniques developed in this study will be of great benefit to future studies utilizing similar methods.

Multispectral visible and near infrared (VNIR) observations from the Mars Exploration Rover Pancam multispectral stereo camera systems are consistent with materials having been subjected to various aqueous processes. Ferric oxides in the form of hematite in the Burns and Grasberg formations of Meridiani Planum have been well characterized by Opportunity on the basis of strong 535 and 864 nm absorptions and positive 754–1009 nm and 934–1009 nm slopes. On the rim of Noachian-aged Endeavour crater, Opportunity has observed light-toned veins with high Ca and S, as determined by the rover’s Alpha Particle X-ray Spectrometer (APXS), and a negative 934–1009 nm slope in VNIR spectra extracted from Pancam data, indicative of a 1000 nm H 2 O overtone absorption. Together these observations indicate that the veins are composed of gypsum. Rocks overturned by Opportunity on the Murray Ridge portion of the Endeavour crater rim display dark- and light-toned coatings. The dark-toned coatings have a red, featureless slope that is consistent with the slope observed in laboratory spectra of high-valence manganese oxide minerals. Potential Mn oxide coatings may also be associated with some exposures of the Grasberg formation. APXS results for high Mg and S in the light-toned coatings of the Murray Ridge overturned rocks and a negative 934–1009 nm slope are consistent with hydrated Mg-sulfates. Opportunity has also observed spectral features in rocks that are consistent with orbital observations of Fe-smectites, as well as Al-smectites and possible hydrated silica in light-toned fracture-fill materials. The Spirit rover observed sulfate-rich light-toned soils exposed by the rover’s wheels. Several of these soil observations contained spectral features, such as a broad absorption centered near 800 nm, consistent with ferric sulfate minerals, a finding confirmed by the rover’s Mössbauer spectrometer. Spirit also excavated light-toned Si-rich soils. These soils have a flat near-infrared spectrum with a drop in reflectance from 934–1009 nm that is consistent with free water contained in voids or adsorbed onto the surface of the silica.

To study the kinetics of the spinel-to-garnet transformation in peridotite, we conducted reaction experiments in the garnet peridotite stability field (3.2 GPa, 1020–1220 °C, for 0.6–30 h) using a single spinel crystal embedded in monomineralic orthopyroxene powder or in a mixture of powdered orthopyroxene and clinopyroxene. The growth textures observed in the reaction rim between the spinel crystal and the polycrystalline pyroxenes show that the reaction rim grew in both the spinel and pyroxenes directions, suggesting mobility of both SiO 2 and R 2 O 3 components (where R is a trivalent cation). Olivine grains formed only in the presence of monomineralic orthopyroxene and were present in some domains without forming reaction rims. Based on a diffusion-controlled growth model, the growth kinetics of the garnet reaction rim can be described by [ x ( t )] 2 = k 0 exp(– H */R T ) t , where x ( t ) is the rim width at time t , R is the gas constant, T is the absolute temperature, and H * is the activation enthalpy of reaction; k 0 and H * are, respectively, k 0 = 10 −19.8 ± 4.9 m 2 /s and H * = 171 ± 58 kJ/mol. The development of a garnet reaction rim around a spinel core has been observed in alpine-type peridotitic rocks and mantle xenoliths. The reaction rims experimentally produced in this study are characteristic of corona textures observed in natural rocks, and the experimentally measured growth rate of the rims places important constraints on dynamic transformation processes involving spinel and garnet in peridotite. However, to reconstruct the P-T-t history of the corona texture based on these elementary processes, additional detailed studies on the textural evolution and quantitative kinetics of the garnetrim growth stage are required.

Understanding the thermodynamics of liquid silicates at high pressure and temperature is essential for many petrologic problems, and sodium aluminosilicates are an important component of most magmatic systems. We provide a high-pressure equation of state (EOS) for liquid NaAlSi 3 O 8 based upon molecular dynamics (MD) simulations. The resulting thermodynamic properties have changes in pressure and temperature correlative to trends in diffusion and atomic structure, giving insight to the connections between macroscopic and microscopic properties. Internal pressure shows a maximum in attractive interatomic forces at low pressure, giving way to the dominance of repulsive forces at higher pressure. Self-diffusion coefficients ( D ) typically order D Na > D A1 > D O > D Si . At the lowest temperature, self-diffusivity (anomalously) increases as pressure increases up to ~5–6 GPa for Al, Si, and O. Diffusion data outside this “anomalous” region are fit by a modified Arrhenius expression, from which activation energies are calculated: 85 kJ/mol (Na) to 140 kJ/mol (Si). The amount of AlO 4 and SiO 4 polyhedra (tetrahedra) decreases upon compression and is approximately inversely correlated to the abundance of five- and sixfold structures. Average coordination numbers for Al-O, O-O, and Na-O polyhedra increase sharply at low pressure but start to stabilize at higher pressure, corresponding to changes in interatomic repulsion forces as measured by the internal pressure. High-pressure repulsion also correlates with a close-packed O-O structure where ~12 O atoms surround a central O. Self-diffusivity stabilizes at higher pressures as well. Relationships between the internal pressure, self-diffusion, and structural properties illustrate the link between thermodynamic, transport, and structural properties of liquid NaAlSi 3 O 8 at high pressure and temperature, shedding light on how microscopic structural changes influence macroscopic properties in molten aluminosilicates.

Life on Earth shows preference toward the set of organics with particular spatial configurations. Enantiomeric excesses have been observed for α-methyl amino acids in meteorites, which suggests that chiral asymmetry might have an abiotic origin. A possible abiotic mechanism that could produce chiral asymmetry in meteoritic amino acids is their formation under the influence of asymmetric catalysts, as mineral crystallization can produce spatially asymmetric structures. Although magnetite plaquettes have been proposed to be a possible candidate for an asymmetric catalyst, based on the suggestion that they have a spiral structure, a comprehensive description of their morphology and interpretation of the mechanism associated with symmetry-breaking in biomolecules remain elusive. Here we report observations of magnetite plaquettes in carbonaceous chondrites (CC) that were made with scanning electron microscopy and synchrotron X-ray computed microtomography (SXRCT). We obtained the crystal orientation of the plaquettes using electron backscatter diffraction (EBSD) analysis. SXRCT permits visualization of the internal features of the plaquettes. It provides an unambiguous conclusion that the plaquettes are devoid of a spiral feature and, rather that they are stacks of individual magnetite disks that do not join to form a continuous spiral. Despite the lack of spiral features, our EBSD data show significant changes in crystal orientation between adjacent magnetite disks. The magnetite disks are displaced in a consistent relative direction that lead to an overall crystallographic rotational mechanism. This work offers an explicit understanding of the structures of magnetite plaquettes in CC, which provides a fundamental basis for future interpretation of the proposed symmetry-breaking mechanism.

The mineral loparite is the principal ore of the light rare earth elements (LREE) with solid solution compositions in the quaternary system perovskite-lueshite-tausonite-loparite (CaTiO 3 -NaNbO 3 -SrTiO 3 -Na 0.5 Ln 0.5 TiO 3 ) ( Ln = La, Ce, Pr, Nd). In this study, perovskite solid solutions Ca 1-2x Na x La x TiO 3 (0 ≤ x ≤ 0.50) along the perovskite-loparite join were synthesized using solid-state sintering methods. XRD analysis indicates that as the Na+La content increases, the structure changes from orthorhombic to tetragonal. The enthalpies of formation at 298 K from the constituent oxides (Δ H ° f, ox ) and from the elements (Δ H ° f, el ) have been determined using high-temperature oxide melt solution calorimetry in molten 3Na 2 O.4MoO 3 at 973 K. Enthalpy of formation from oxides Δ H ° f, ox becomes more exothermic with increasing Na+La content, suggesting a stabilization effect of the substitution Ca 2+ → 0.5Na + + 0.5La 3+ . The observed trend of increasing thermodynamic stability with decreasing structural distortion is in agreement with that seen in many other ABO 3 perovskites. The thermodynamic stability of perovskite solid solutions Ca 1-2x Na x La x TiO 3 (0 ≤ x ≤ 0.50) along the CaTiO 3 -Na 0.5 La 0.5 TiO 3 join provides insights into the natural occurrence of loparite minerals (La, Na, Sr, Ca)(Ti, Nb, Ta, Fe 3+ )O 3 .

Fe 3+ minerals are ubiquitous in diverse near-surface environments, where they exert important controls on trace species transport. In alkaline environments such as the glass-steel interface in geological high-level radioactive waste disposal sites that use cement for plugging and grouting, Fe minerals are closely associated with Si that may affect their crystallization behavior as well as their capacities to regulate hazardous element cycling. While it is well known that Si retards Fe mineral crystallization, there is currently an overall lack of quantitative information on the rates of crystallization of stable Fe minerals in the presence of Si at alkaline conditions. Crystallization of Fe 3+ minerals goethite and hematite from ferrihydrite co-precipitated with different amounts of Si was studied at pH 10 and at temperatures ranging from 50 to 80 °C using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Mineral abundances evaluated from Rietveld refinement of XRD data show that the proportion of goethite in the final assemblage decreases relative to hematite with increasing Si. TEM observation of goethite and hematite crystals formed in the presence of Si show significant morphological differences compared to those formed in the absence of Si. Rate constants for crystallization derived from fitting of time-dependent changes in mineral abundances with the Avrami equation show a decreasing trend with increasing Si for both goethite and hematite. Apparent activation energies for crystallization for both minerals increase with increasing Si, with that of goethite increasing more drastically compared to hematite, indicating the inhibitive effect of Si on the crystallization of both minerals. The overall inhibition of crystallization may be explained in terms of the effects of Si on the surface properties of the ferrihydrite precursor. The rate constants and apparent activation energies reported in this study may be useful in estimating the crystallization behavior and timescales of Fe minerals in both natural and engineered environments. This information may eventually be helpful in predicting the fate of hazardous elements in such environments.

Dusty olivine (olivine containing multiple sub-micrometer inclusions of metallic iron) in chondritic meteorites is considered an ideal carrier of paleomagnetic remanence, capable of maintaining a faithful record of pre-accretionary magnetization acquired during chondrule formation. Here we show how the magnetic architecture of a single dusty olivine grain from the Semarkona LL3.0 ordinary chondrite meteorite can be fully characterized in three dimensions, using a combination of focused ion beam nanotomography (FIB-nT), electron tomography, and finite-element micromagnetic modeling. We present a three-dimensional (3D) volume reconstruction of a dusty olivine grain, obtained by selective milling through a region of interest in a series of sequential 20 nm slices, which are then imaged using scanning electron microscopy. The data provide a quantitative description of the iron particle ensemble, including the distribution of particle sizes, shapes, interparticle spacings and orientations. Iron particles are predominantly oblate ellipsoids with average radii 242 ± 94 × 199 ± 80 × 123 ± 58 nm. Using analytical TEM we observe that the particles nucleate on sub-grain boundaries and are loosely arranged in a series of sheets parallel to (001) of the olivine host. This is in agreement with the orientation data collected using the FIB-nT and highlights how the underlying texture of the dusty olivine is crystallographically constrained by the olivine host. The shortest dimension of the particles is oriented normal to the sheets and their longest dimension is preferentially aligned within the sheets. Individual particle geometries are converted to a finite-element mesh and used to perform micromagnetic simulations. The majority of particles adopt a single vortex state, with “bulk” spins that rotate around a central vortex core. We observed no particles that are in a true single domain state. The results of the micromagnetic simulations challenge some preconceived ideas about the remanence-carrying properties of vortex states. There is often not a simple predictive relationship between the major, intermediate, and minor axes of the particles and the remanence vector imparted in different fields. Although the orientation of the vortex core is determined largely by the ellipsoidal geometry (i.e., parallel to the major axis for prolate ellipsoids and parallel to the minor axis for oblate ellipsoids), the core and remanence vectors can sometimes lie at very large (tens of degrees) angles to the principal axes. The subtle details of the morphology can control the overall remanence state, leading in some cases to a dominant contribution from the bulk spins to the net remanence, with profound implications for predicting the anisotropy of the sample. The particles have very high switching fields (several hundred millitesla), demonstrating their high stability and suitability for paleointensity studies.

Thermally activated dislocation glide in Mg 2 SiO 4 wadsleyite at 15 GPa has been modeled to investigate its potential contribution to plastic deformation of wadsleyite in the Earth’s transition zone. Modeling is based on a multiphysics approach that allows calculating the constitutive equations associated with single slip for a wide range of temperatures and strain rates typical for the laboratory and the Earth’s mantle. The model is based on the core structures of the rate limiting ½<111>{101} and [100](010) dissociated screw dislocations. After quantifying their lattice friction, glide is modeled through an elastic interaction model that allows calculating the critical configurations that trigger elementary displacements of dissociated dislocations. The constitutive relations corresponding to glide are then deduced with Orowan’s equation to describe the average intracrystalline plasticity. The high stresses predicted by the model are found to be in good agreement with experimental data on plastic deformation of wadsleyite at high-pressure conditions. Moreover, it is found that even at appropriate mantle strain rates, glide of dislocations remain difficult with critical resolved shear stress (CRSS) values typically larger than 100 MPa. This implies the inefficiency of dislocation glide to the overall plastic deformation of Mg 2 SiO 4 wadsleyite under transition zone conditions.

The new minerals carlsonite (IMA2014-067), (NH4)5Fe33+O(SO4)6⋅7H2O${{\rm{(N}}{{\rm{H}}_{\rm{4}}}{\rm{)}}_{\rm{5}}}{\rm{Fe}}_3^{3 + }{\rm{O(S}}{{\rm{O}}_{\rm{4}}}{{\rm{)}}_{\rm{6}}} \cdot {\rm{7}}{{\rm{H}}_{\rm{2}}}{\rm{O}}$ , and huizingite-(Al) (IMA2015-014), (NH 4 ) 9 Al 3 (SO 4 ) 8 (OH) 2 ·4H 2 O, formed from a natural fire in an oil-bearing shale near Milan, Ohio. Carlsonite crystals are yellow to orange-brown thick tablets, flattened on {001}, or stout prisms, elongated on [110], up to about 0.5 mm in size. The mineral has a tan streak, vitreous luster, Mohs hardness of 2, brittle tenacity, irregular fracture, perfect {001} cleavage, calculated density of 2.167 g/cm 3 , and is easily soluble in H 2 O. Carlsonite is optically biaxial (–), a = 1.576(1), b = 1.585(1), and g = 1.591(1) (white light). Huizingite-(Al) crystals, typically intergrown in light greenish yellow drusy aggregates, are tabular to bladed, flattened on {100}, up to about 0.25 mm in maximum dimension. The mineral has a white streak, vitreous luster, Mohs hardness of 2, brittle tenacity, irregular fracture, no cleavage, calculated density of 2.026 g/cm 3 , and is easily soluble in H 2 O. Huizingite-(Al) is optically biaxial (+) with a = 1.543(1), b = 1.545(1), and g = 1.563(1) (589.6 nm light). Raman and infrared spectroscopy was conducted on both minerals. Electron microprobe analyses provided the empirical formulas [(NH4)4.64Na0.24K0.12]∑5.00Fe3.053+O(SO4)6⋅6.93H2O${{\rm{[(N}}{{\rm{H}}_{\rm{4}}}{{\rm{)}}_{{\rm{4}}{\rm{.64}}}}{\rm{N}}{{\rm{a}}_{{\rm{0}}{\rm{.24}}}}{{\rm{K}}_{{\rm{0}}{\rm{.12}}}}{\rm{]}}_{\sum 5.00}}{\rm{Fe}}_{3.{\rm{05}}}^{3 + }{\rm{O(S}}{{\rm{O}}_{\rm{4}}}{{\rm{)}}_{\rm{6}}} \cdot 6.93{{\rm{H}}_2}{\rm{O}}$ and [(NH4)8.76Na0.22K0.02]∑9.00(Al1.65Fe1.343+)∑2.99(OH)1.98(H2O)4.02(SO4)8.00${{\rm{[(N}}{{\rm{H}}_{\rm{4}}}{{\rm{)}}_{{\rm{8}}{\rm{.76}}}}{\rm{N}}{{\rm{a}}_{{\rm{0}}{\rm{.22}}}}{{\rm{K}}_{{\rm{0}}{\rm{.02}}}}{\rm{]}}_{\sum {\rm{9}}{\rm{.00}}}}{{\rm{(A}}{{\rm{l}}_{{\rm{1}}{\rm{.65}}}}{\rm{Fe}}_{{\rm{1}}{\rm{.34}}}^{{\rm{3 + }}}{\rm{)}}_{\sum {\rm{2}}{\rm{.99}}}}{\rm{ (OH}}{{\rm{)}}_{{\rm{1}}{\rm{.98}}}}{{\rm{(}}{{\rm{H}}_{\rm{2}}}{\rm{O)}}_{{\rm{4}}{\rm{.02}}}}{{\rm{(S}}{{\rm{O}}_{\rm{4}}}{\rm{)}}_{{\rm{8}}{\rm{.00}}}}$ for carlsonite and huizingite-(Al), respectively. Huizingite compositions with Fe > Al were noted. Carlsonite is triclinic, P1, a = 9.5927(2), b = 9.7679(3), c = 18.3995(13) Å, α = 93.250(7)°, β = 95.258(7)°, γ = 117.993(8)°, V = 1506.15(16) Å 3 , and Z = 2. Huizingite-(Al) is triclinic, P 1¯$\bar 1$, a = 9.7093(3) b = 10.4341(3), c = 10.7027(8) Å, α = 77.231(5)°, β = 74.860(5)°, γ = 66.104(5)°, V = 948.73(9) Å 3 , and Z = 1. The five strongest lines in the X-ray powder diffraction pattern of carlsonite are [ d obs in Å( I )( hkl )]. 9.23(100)(002); 8.26(40)(100,011); 7.57(43)(1¯$\bar 1$11,11¯$\bar 1$1,011); 4.93(23)(1¯$\bar 1$1¯$\bar 1$, 1¯$\bar 1$20); and 3.144(41)(multiple). Those for huizingite-(Al) are: 8.82(60)(100); 5.04(69)(121); 3.427(100)(2¯$\bar 2$2¯$\bar 2$1); 3.204(68)(2¯$\bar 2$11); and 3.043(94)(21¯$\bar 1$2,312). The crystal structures of carlsonite ( R 1 = 0.030) and huizingite ( R 1 = 0.040) are bipartite, each consisting of a structural unit and an interstitial unit. For carlsonite, the structural unit is a [Fe33+O(H2O)3(SO4)6]5−${[{\rm{Fe}}_3^{3 + }{\rm{O(}}{{\rm{H}}_{\rm{2}}}{\rm{O}}{{\rm{)}}_{\rm{3}}}{{\rm{(S}}{{\rm{O}}_{\rm{4}}}{\rm{)}}_{\rm{6}}}{\rm{]}}^{{{\rm{5}}^ - }}}$ cluster and the interstitial complex is [(NH 4 ) 5 (H 2 O) 4 ] 5 +. For huizingite-(Al), the structural unit is a [(Al, Fe 3 +) 3 (OH) 2 (H 2 O) 4 (SO 4 ) 6 ] 5− cluster and the interstitial complex is [(NH 4 ) 9 (SO 4 ) 2 ] 5 +. In the carlsonite cluster, three FeO 6 octahedra share a common vertex, while in the huizingite-(Al) cluster, three (Al, Fe)O 6 octahedra form an abbreviated corner-linked chain. The cluster in carlsonite is the same as that in metavoltine, while the huizingite-(Al) cluster is unique. The range of Lewis basicity of the structural unit in carlsonite is 0.23–0.11 valence units (v.u.) and in huizingite-(Al) it is 0.20–0.12 v.u.; the corresponding Lewis acidities of the interstitial complexes in these structures are 0.13 and 0.14 v.u., respectively. A characteristic Lewis acid strength of 0.13 v.u. is suggested for NH4+${\rm{NH}}_{\rm{4}}^ + $ when it is in its most typical coordinations of 7 to 8. The close structural relationship between carlsonite and metavoltine and the similarity of their powder diffraction patterns suggests that carlsonite may have misidentified as metavoltine in some NH 4 -rich mineral assemblages. The new heteropolyhedral cluster in the structure of huizingite-(Al) is of interest because its existence may provide insights into the structural and paragenetic relations among hydrated ferric sulfate minerals. In particular, it may exist as a complex in aqueous solutions or in solid-state transformations involving the formation and/or breakdown of sideronatrite-style [Fe 3 +(SO 4 ) 3 ] 3− chains. We surmise that it may be a more commonly formed mineral than its abundance would indicate and that its rarity may reflect a narrow stability range, and so a transitory existence.

The system B 2 O 3 -Al 2 O 3 -SiO 2 (BAS) includes two ternary phases occurring naturally, boromullite, Al 9 BSi 2 O 19 , and boralsilite, Al 16 B 6 Si 2 O 37 , as well as synthetic compounds structurally related to mullite. The new mineral vránaite, a third naturally occurring anhydrous ternary BAS phase, is found with albite and K-feldspar as a breakdown product of spodumene in the elbaite-subtype Manjaka granitic pegmatite, Sahatany Valley, Madagascar. Boralsilite also occurs in this association, although separately from vránaite; both minerals form rare aggregates of subparallel prisms up to 100 μm long. Optically, vránaite is biaxial (–), n α = 1.607(1), n β = 1.634(1), n γ = 1.637(1) (white light), 2 V x (calc) = 36.4°, X ≈ c ; Y ≈ a ; Z = b . An averaged analysis by EMP and LA-ICP-MS (Li, Be) gives (wt%) SiO 2 20.24, B 2 O 3 11.73, Al 2 O 3 64.77, BeO 1.03, MnO 0.01, FeO 0.13, Li 2 O 1.40, Sum 99.31. Raman spectroscopy in the 3000–4000 cm −1 region rules out the presence of significant OH or H 2 O. Vránaite is monoclinic, space group I 2/ m , a = 10.3832(12), b = 5.6682(7), c = 10.8228(12) Å, β = 90.106(11)°; V = 636.97(13) Å 3 , Z = 1. In the structure [ R 1 = 0.0416 for 550 F o > 4σ F o ], chains of AlO 6 octahedra run parallel to [010] and are cross-linked by Si 2 O 7 disilicate groups, BO 3 triangles, and clusters of AlO 4 and two AlO 5 polyhedra. Two Al positions with fivefold coordination, Al4 and Al5, are too close to one another to be occupied simultaneously; their refined site-occupancy factors are 54% and 20% occupancy, respectively. Al5 is fivefold-coordinated Al when the Al9 site and both O9 sites are occupied, a situation giving a reasonable structure model as it explains why occupancies of the Al5 and O9 sites are almost equal. Bond valence calculations for the Al4 site suggest Li is likely to be sited here, whereas Be is most probably at the Al5 site. One of the nine O sites is only 20% occupied; this O9 site completes the coordination of the Al5 site and is located at the fourth corner of what could be a partially occupied BO 4 tetrahedron, in which case the B site is shifted out of the plane of the BO 3 triangle. However, this shift remains an inference as we have no evidence for a split position of the B atom. If all sites were filled (Al4 and Al5 to 50%), the formula becomes Al 16 B 4 Si 4 O 38 , close to Li 1.08 Be 0.47 Fe 0.02 Al 14.65 B 3.89 Si 3.88 O 36.62 calculated from the analyses assuming cations sum to 24. The compatibility index based on the Gladstone-Dale relationship is 0.001 (“superior”). Assemblages with vránaite and boralsilite are inferred to represent initial reaction products of a residual liquid rich in Li, Be, Na, K, and B during a pressure and chemical quench, but at low H2O activities due to early melt contamination by carbonate in the host rocks. The two BAS phases are interpreted to have crystallized metastably in lieu of dumortierite in accordance with Ostwald Step Rule, possibly first as “boron mullite,” then as monoclinic phases. The presence of such metastable phases is suggestive that pegmatites crystallize, at least partially, by disequilibrium processes, with significant undercooling, and at high viscosities, which limit diffusion rates.

The thermoluminescence behavior of long-range ordered crystals is usually explained by the band structure model, using first- and second-order kinetics. However, feldspars have order-disorder phenomena and twinning, and consequently these mathematical descriptions are not helpful in most cases. In this work, the thermally stimulated intrinsic blue luminescence at 440 nm from X-ray induced defects of the K-rich feldspars is used to show a progressive behavior change along the order-disorder series. It is observed a gradual conversion of the TL signal from a very asymmetric peak with exponential rise and power law decay in microcline and orthoclase, where a t coefficient in log-log plots decreases with twin/domain size, to a more symmetric signal in a partially disordered sanidine, up to reach a completely symmetric Gaussian peak in fully disordered sanidine. These results are compatible with the Bässler’s model of disorder, which suggest that atomic disorder involves the transformation of delocalized bands first into band tails as the source of electron traps, and later in localized density of states following a Gaussian distribution.