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Direct analysis of the composition of Mars is possible through delivery of meteorites to Earth. Martian meteorites include ∼165 to 2400 Ma shergottites, originating from depleted to enriched mantle sources, and ∼1340 Ma nakhlites and chassignites, formed by low degree partial melting of a depleted mantle source. To date, no unified model has been proposed to explain the petrogenesis of these distinct rock types, despite their importance for understanding the formation and evolution of Mars. Here we report a coherent geochemical dataset for shergottites, nakhlites and chassignites revealing fundamental differences in sources. Shergottites have lower Nb/Y at a given Zr/Y than nakhlites or chassignites, a relationship nearly identical to terrestrial Hawaiian main shield and rejuvenated volcanism. Nakhlite and chassignite compositions are consistent with melting of hydrated and metasomatized depleted mantle lithosphere, whereas shergottite melts originate from deep mantle sources. Generation of martian magmas can be explained by temporally distinct melting episodes within and below dynamically supported and variably metasomatized lithosphere, by long-lived, static mantle plumes.

Secondary ion mass spectrometry was used to test the δ18O and δ34S nanogram‐scale homogeneity of a suite of candidate sulfate minerals, ultimately selecting three barite, two anhydrite, and two gypsum samples from the Royal Ontario Museum that have repeatabilities for their SIMS measurements of better than ±0.39‰ and ±0.37‰ (1s) for oxygen and sulfur isotope ratios, respectively. Metrological splits of each of the seven materials were sent to multiple gas source isotope ratio mass spectrometry laboratories in order to establish their absolute 18O/16O and 34S/32S ratios. The inter‐laboratory results of GS‐IRMS analyses yielded reasonably narrow ranges in δ18OVSMOW, whereas larger variations in δ34SVCDT values were found between the results from the gas source laboratories. All samples have good reproducibility within laboratories of GS‐IRMS 103δ18O values of between ±0.24‰ and ±0.44‰ (1s). The reproducibility within laboratories of GS‐IRMS 103δ34S values range from ±0.07‰ to ±0.99‰ (1s). Here we also discuss some of the current analytical limitations affecting these isotope‐mineral systems. A total of 256 metrological splits have been prepared from each of these seven materials; these aliquots will be made available to the global geochemical community. [ABSTRACT FROM AUTHOR]

The matrix of the C2‐ungrouped Tarda meteorite contains abundant smectite minerals that swell and crumble when exposed to polar liquids, causing the sample to rapidly slake. This phenomenon presents a serious challenge when polishing the meteorite, as common polishing liquids used on carbonaceous chondrites, such as water, ethanol, ethylene glycol, and isopropyl alcohol, are polar and will cause the sample to swell, making it unsuitable for some analyses. Hexane and mineral oil are nonpolar liquids that were found to not induce swelling on highly expansive montmorillonite‐clay analog material and were effectively integrated into a polishing procedure for Tarda. Here, we detail a procedure for mounting, cutting, and polishing the Tarda meteorite to prepare a surface that is suitable for a variety of sensitive techniques, such as electron microprobe analysis. This work offers a practical methodology for the preparation of other clay‐rich samples, which may include the recently returned Ryugu and Bennu materials. [ABSTRACT FROM AUTHOR]

Esperite from Franklin, New Jersey, was first described by Moore and Ribbe (1965) as monoclinic with a well-developed 'superlattice' a = 2 x 8.814(2) [Angstrom], b = 8.270(3)[Angstrom], c = 2 x 15.26(1)[Angstrom], [beta] [approximately equal to] 90[degrees], space group [P2.sub.1]/n (subcell), and the chemical formula Pb[Ca.sub.3][(ZnSi[O.sub.4]).sub.4]. They attributed 'superlattice' reflections to the ordered distributions of Pb and Ca cations over four beryllonite-type subcells for esperite with the Ca:Pb ratio greater than 2:1. We examined two esperite fragments from the type sample using single-crystal X-ray diffraction, electron microprobe analysis, and Raman spectroscopy. Although both fragments have Ca:Pb [approximately equal to] 1.8, one exhibits the 'superlattice' reflections as observed by Moore and Ribbe (1965), whereas the other does not. The sample without 'superlattice' reflections has unit-cell parameters a = 8.7889(2), b = 8.2685(2), c = 15.254(3) [Angstrom], [beta] = 90.050[(1).sup.o], V = 1108.49(4) [[Angstrom].sup.3], and the chemical composition [Pb.sup.1.00]([Ca.sup.1.86][Fe.sup.2+.sub.0.07][Mn.sub.0.04] [Cr.sup.3+.sub.0.02]).sub.[[summation] = 1.99] [([Zn.sub.1.00][Si.sub.1.00][O.sub.4]).sub.3]. Its crystal structure was solved in space group [P2.sub.1]/n ([R.sub.1] = 0.022). Esperite is isostructural with beryllonite, NaBeP[O.sub.4], and its ideal chemical formula should, therefore, be revised to Pb[Ca.sub.2][(ZnSi[O.sub.4]).sub.3], Z = 4. The Zn[O.sub.4] and Si[O.sub.4] tetrahedra in esperite share corners to form an ordered framework, with [Pb.sup.2+] occupying the nine-coordinated site in the large channels and [Ca.sup.2+] occupying the two distinct octahedral sites in the small channels. The so-called 'superlattice' reflections are attributed to triple twins, a trilling of ~60[degrees] rotational twinning around the b axis, similar to those observed in many other beryllonite-type materials. A phase transformation from a high-temperature polymorph to the esperite structure is proposed to be responsible for the twinning formation. Keywords: Esperite, beryllonite, Pb-Zn silicates, crystal chemistry, X-ray diffraction DOI: 10.2138/am.2010.3415

Dellaventuraite is a new amphibole species from the Kajlidongri manganese mine, Jhabua District, Madhya Pradesh, India. It occurs with leakeite, kornite, albite, braunite, and bixbyite associated with cross-cutting epigenetic veins that have reacted with regionally metamorphosed rocks containing Mn-rich minerals (braunite, bixbyite, jacobsite, spessartine) to produce Mn-rich amphiboles, Mn-rich pyroxenes, Mn-rich mica, piemontite, and manganophyllite. Dellaventuraite occurs as anhedral grains, the color of which varies from pink to red, depending on Mn content. It is brittle, H = 5, [D.sub.calc] = 3.184 g/[cm.sup.3], has a pale pink streak, vitreous luster, and does not fluoresce in ultraviolet light; it has perfect cleavage on {110} and conchoidal fracture. In transmitted plane-polarized light, dellaventuraite is strongly pleochroic, X = pale mauve-brown. Y ~ Z = dark red-brown: Y ^ a = 20[degrees] (in [beta] obtuse), Z = b, with absorption X < Y ~ Z. It is biaxial positive, [[eta].sub.[alpha]] = 1.688 [+ or -] 0.003, [[eta].sub.[beta]] = 1.692 [+ or -] 0.005, [[eta].sub.[gamma]] = 1.721 [+ or -] 0.003, 2[V.sub.(obs)] = 49 [+ or -] 3[degrees], 2[V.sub.(calc)] = 41[degrees]. Dellaventuraite is monoclinic, space group C2/m, a = 9.808(1), b = 17.840(2), c = 5.2848(5) [angstrom], [gamma] = 104.653(1)[degrees], V = 894.6(2) [[angstrom].sup.3], Z = 2. The strongest ten X-ray diffraction lines in the powder pattern are [d(l,hkl)]: 2.697(10,151), 2.542(9,-202), 3.127(8,310), 3.378(7,131), 2.154(7,261), 1.434 (7.-661), 4.450(6,021), 8.459(5,110), 2.727(5,-331), 2.328(5,-351). Analysis by a combination of electron microprobe, SIMS and crystal-structure refinement gives Si[O.sub.2] = 54.22, [Al.sub.2][O.sub.3] = 0.81, Ti[O.sub.2] = 5.45, [Fe.sub.2][O.sub.3] = 6.44, [Mn.sub.2][O.sub.3] = 7.57. ZnO = 0.12, NiO = 0.16, MgO = 8.26, [Li.sub.2]O = 1.53, CaO = 1.85, [Na.sub.2]O = 8.12, [K.sub.2]O = 2.12, [H.sub.2]O = 0.80, Cr, V, F, Cl not detected, sum 97.41 wt%. The formula unit, calculated on the basis of 24(O,OH,F) is ([K.sub.0.40][Na.sub.0.61])([Na.sub.1.71][Ca.sub.0.29]) ([Mg.sub.1.81][Zn.sub.0.01][Ni.sub.0.02][Li.sub.0.90] [Fe.sup.3+.sub.0.71][Mn.sup.3+.sub.0.85][Ti.sup.4+.sub.0.60] [Al.sub.0.10])([Si.sub.7.96][Al.sub.0.04])[O.su b.22][[(OH).sub.0.80] [O.sub.1.20]; the ideal end-member composition Na[Na.sub.2](Mg[Mn.sup.3+][sub.2]Li[Ti.sup.4+])[Si.sub.8] [O.sub.22][O.sub.2]. The crystal structure of dellaventuraite was refined to an R index of 3.8% using MoK[alpha] X-ray intensity data. The M1 site is occupied by [Ti.sup.4+], [Mn.sup.3+], and Mg in approximately equal amounts, the M2 site is occupied primarily by Mg and [Fe.sup.3+], and M3 is occupied by Li with minor Mg and [Mn.sup.2+]. Local bond-valence considerations suggest that [O.sup.2-] at O3 is linked to [Ti.sup.4+]Mg or [Mn.sup.3+][Mn.sup.3+] at the adjacent M1 sites, and that OH at O3 is linked to MgMg at the adjacent M1 sites.

Kinetic studies are reported of the effect of methanol on the rate of formation of C[O.sub.2]--and C[H.sub.4]--hydrates by means of in situ time-of-flight neutron powder diffraction. The experiments were carried out at temperatures ranging from 200 to 250 K and pressures up to 7 MPa. The samples were prepared from mixtures of ground, deuterated ice and deuterated methanol (up to 20 vol%), which were transformed in situ into C[O.sub.2]--or C[H.sub.4]--hydrates by pressurizing the systems with the corresponding gas. The observed rates of formation of hydrates are orders of magnitude higher than the rate of formation from pure deuterated ice under the same pressure and temperature conditions. Glycols and alcohols, methanol in particular, are long known as thermodynamic inhibitors of hydrate formation. Our study indicates that methanol can also act as a kinetic promoter for the formation of gas hydrates. Preliminary data suggest that the kinetics also depend strongly on concentration and the isotopic composition.

Northwest Africa (NWA) 869 is the largest sample of chondritic regolith breccia, making it an ideal source for research on accretionary processes and primordial chemical mixing. One such process can be seen in detail through the first identification of a eucrite impactor clast in an L chondrite breccia. The ~7 mm diameter clast has oxygen isotope compositions (Δ17O = −0.240, −0.258‰) and pigeonite and augite compositions typical for eucrites, but with high areal abundance of silica (9.5%) and ilmenite (1.5%). The rim around the clast is a mixture of breccia and igneous phases, the latter due to either impactor‐triggered melting or later metamorphism. The rim has an oxygen isotope composition falling on a mixing line between known eucrite and L chondrite compositions (Δ17O = 0.326‰) and, coincidentally, on the Mars fractionation line. Pyroxene grains from the melt component in the rim have compositions that fall on a mixing line between the average eucrite pyroxene composition and equilibrated L chondrite composition. The margins of chondritic olivine crystal clasts in the rim are enriched in Fe as a result of diffusion from the Fe‐rich melt and suggest cooling on the scale of hours. The textures and chemical mixing observed provide evidence for an unconsolidated L chondrite target material, differing from the current state of NWA 869 material. The heterogeneity of oxygen isotope and chemical signatures at this small length scale serve as a cautionary note when extrapolating from small volumes of materials to deduce planetesimal source characteristics. [ABSTRACT FROM AUTHOR]

In situ neutron inelastic scattering experiments on hydrogen adsorbed into a fully deutrated tetrahydrofuran-water ice clathrate show that the adsorbed hydrogen has three rotational excitations (transitions between J=0 and 1 states) at approximately 14 meV in both energy gain and loss. These transitions could be unequivocally assigned since there was residual orthohydrogen at low temperatures (slow conversion to the ground state) resulting in an observable J=1→0 transition at 5 K (kT=0.48 meV). A doublet in neutron energy loss at approximately 28.5 meV is interpreted as J=1→2 transitions. In addition to the transitions between rotational states, there are a series of peaks that arise from transitions between center-of-mass translational quantum states of the confined hydrogen molecule. A band at approximately 9 meV can be unequivocally interpreted as a transition between translational states, while broad features at 20, 25, 35, and 50–60 meV are also interpreted to as transitions between translational quantum states. A detailed comparison is made with a recent five-dimensional quantum treatment of hydrogen in the smaller dodecahedral cage in the SII ice-clathrate structure. Although there is broad agreement regarding the features such as the splitting of the J=1 degeneracy, the magnitude of the external potential is overestimated. The numerous transitions between translational states predicted by this model are in poor agreement with the experimental data. Comparisons are also made with three simple exactly solved models, namely, a particle in a box, a particle in a sphere, and a particle on the surface of a sphere. Again, there are too many predicted features by the first two models, but there is reasonable agreement with the particle on a sphere model. This is consistent with published quantum chemistry results for hydrogen in the dodecahedral 512 cage, where the center of the cage is found to be energetically unfavorable, resulting in a shell-like confinement for the hydrogen molecule wave function. These results demonstrate that translational quantum effects are very significant and a classical treatment of the hydrogen molecule dynamics is inappropriate under such conditions. [ABSTRACT FROM AUTHOR]