Lunar Ilmenite Research Articles

Experiments on thermal release of implanted noble gases from minerals and their implications for noble gases in lunar soil grains

Experiments on ion implantation were performed in order to study the release mechanisms of solar particles from lunar soil grains. Helium, neon, and argon ions were implanted into olivine and ilmenite. The release temperatures of noble gases were investigated by heating samples stepwise; the results show that they depend on irradiation energy and dose. We conclude that the release temperature is related to the size of bubbles in which noble gases are trapped: Noble gases in small and large bubbles are released at 400–600°C and 800–1200°C, respectively. In Ne and Ar implantation experiments into olivine, a component was released during recrystallization of amorphized surfaces. Based on these experimental results, we suggest that components released from lunar ilmenite grains at different temperatures would correspond to solar particles of different energies. We also suggest that He and Ne of solar wind energy (about 1 keV/amu) should be retained in lunar ilmenite grains, while they should be lost from olivine grains.

Solar‐wind krypton and solid/gas fractionation in the Early Solar Nebula

Krypton is the best candidate for determining limits on solid/gas fractionation in the early sun because of the smoothness of the odd‐mass abundance curve in its mass region, which permits relatively precise interpolations of its abundance assuming no fractionation. Here we calculate the solar‐system Kr abundance from solar‐wind noble‐gas ratios, determined previously by low‐temperature oxidations of lunar ilmenite grains, normalized to Si by spacecraft solar‐wind measurements. The estimated 83Kr abundance of 4.1 ± 1.5 per 106 Si atoms is within uncertainty of estimates assuming no fractionation, determined from CI‐chondrite abundances of surrounding elements. This is significant because it is the first such constraint on solid/gas fractionation, though the large uncertainty only confines it to somewhat less than a factor of two.

Search for solar‐type nitrogen in the gas‐rich Pesyanoe meteorite

Abstract— We report nitrogen isotopic data obtained from a stepwise gas release of two grain‐size fractions of the gas‐rich meteorite Pesyanoe. Cosmic‐ray‐produced 15Nc may be present in all temperature steps ≥600 °C, and we correct this component using spallation 21Ne data. The resulting ratios reveal the presence of more than one trapped N component. Indigenous N is released above 1000 °C with an isotopic signature of δ15N = −33‰. This is consistent with the rather uniform signatures of indigenous nitrogen in enstatite meteorites. There is no evidence for the presence of “very light” N of δ15N ≅ −200‰. On the other hand, a “heavy” nitrogen component appears in the temperature range 700–800 °C, and coincides with a major release of solar‐type noble gases. For a two‐component mixture, the isotopic shifts in this temperature range define a lower limit δ15Ncorr = −6‰ for the second component (e.g., solar‐type nitrogen). However, for the case of a solar‐type component, the calculated δ15N signature depends on the adopted elemental abundances. For example, adoption of the relative abundances of 14N and noble gases in lunar ilmenite 71501 yields δ15N ≅ +170, which is in the range of the heavier nitrogen signatures observed on the lunar surface.

Long-term changes in solar wind elemental and isotopic ratios: A comparison of two lunar ilmenites of different antiquities

An ilmenite separate from lunar regolith breccia 79035, a sample presumed to have been exposed to solar wind more than 2 Ga ago, was analyzed for noble gas and nitrogen elemental and isotopic abundances by stepwise oxidation and pyrolysis. The gases appear to be distributed between two distinct reservoirs in the ilmenite, defined by release patterns and isotopic considerations. One of the reservoirs, near grain surfaces, yields elemental ratios that for the most part are “solar” while the other, sited at greater depths within grains, has severely fractionated elemental abundances and generally heavier isotopic ratios as well. Xenon provides an exception to the solar abundance pattern in the near-surface reservoir, being enhanced by about a factor of 2 relative to the expected value. A comparison of the 79035 separate with a previously analyzed ilmenite from soil 71501, which received its solar wind exposure much more recently, indicates that the two-fold xenon enhancement occurs in the fractionated reservoir as well as the “solar” one, and that it may therefore be attributable to a change in the solar wind elemental abundances. Other differences between the two ilmenites occur in helium and neon isotopic ratios and in He Ar elemental ratios. Since mineralogical influences on retentivities of the gases in the two samples should be the same, and possible contributions of non-solar wind components to one ilmenite in preference to the other can generally be eliminated or accounted for, all of these differences may reflect changes in the solar wind over time.

PIXE microprobe analysis with the Heidelberg proton microprobe

Microprobe analysis with PIXE (“micropixe”) combines advantages of other microprobes. It is a nondestructive method with detection limits at the ppm level. Delicate samples may be altered in cases, where high current densities are used. The content of the trace element Zr in mineral pairs can be used as a geothermometer. The first evidence of the trace elements Sr, Y, and Nb in lunar ilmenites, ulvöspinels, and armalcollites was obtained with the Heidelberg proton microprobe. Preparing a biological sample is a difficult problem. The influence of different preparation methods on elemental distributions in pollen tubes of lilium longiflorum is studied with the micropixe setup in Heidelberg. Knowledge of these influences may help to avoid artefacts during preparation of biological materials for any kind of microprobe analysis.

Cell dimensions and antiferromagnetism of lunar and terrestrial ilmenite single crystals

X-Ray diffraction and anisotropic magnetic measurements have been made on single crystals of lunar ilmenite and on terrestrial ilmenite from Bancroft, Ontario, Canada and the Ilmen Mountains, U.S.S.R. The elongated c -axis of lunar ilmenite, previously reported, is confirmed by new measurements. The shorter c -axis found in terrestrial specimens is ascribed to Fe 3+ substitution for Ti 4+ in the titanium layer. Magnetic measurements on the same specimens show that, in agreement with the Ishikawa-Shirane et al. model, the initial shortening of the c -axis by the above substitution of small amounts of Fe 3+ (<8%) causes an increase in Fe 2+−Fe 2+ exchange coupling through Fe 3+ in the titanium layer that lowers the Néel transition temperature. The Weiss temperatures and other magnetic parameters confirm this model proposed by Ishikawa and Shirane et al. Additional transitions found in one of the terrestrial specimens (Bancroft) have been ascribed to a small amount of an exsolved spinel phase, possibly a solid solution phase of magnetite-ülvospinel. The spinel phase is localized in hematite-rich blebs which exsolved from the host ilmenite-rich phase.

The Néel transition and magnetic properties of terrestrial, synthetic, and lunar ilmenites

The magnetic susceptibility of a terrestrial, synthetic and lunar ilmenite specimen has been measured from 4 to 300 K. All specimens had a single Néel temperature transition which ranged from 56 to 57.7 K. In one case the powdered specimen was partially aligned in the magnetic field prior to the susceptibility measurements and the Néel transition was observed to shift to 60 K indicating magnetic anisotropy. A study of several magnetic parameters calculated from the experimental data showed gross impurities in the terrestrial specimen, single-domain to multi-domain metallic iron in the synthetic specimen, and a small amount of superparamagnetic metallic iron in the lunar sample. No multidomain iron was observed in the lunar ilmenite. The results of electron spin resonance measurements were also in general agreement with these findings. Because of the absence of Fe 3+ compared to most terrestrial samples it is suggested that the anisotropic magnetic parameters be determined on lunar ilmenite when a large enough single crystal becomes available.

An experimental investigation of the significance of zirconium partitioning in lunar ilmenite and ulvöspinel

The partitioning of zirconium between FeTiO 3 and Fe 2TiO 4, in the presence of ZrO 2 + Fe, was determined experimentally in the Fe-Ti-Zr-O system. The ratio of Zr il/Zr usp is strongly temperature dependent. The zirconium concentrations of coexisting ilmenite and ulvöspinel were measured in several Apollo 14 and 15 rocks. These minerals in Apollo 15 rocks contain up to 0.42 and 0.23 wt% Zr, respectively, which are the highest zirconium contents yet reported for these minerals. Although the absolute zirconium concentrations in these phases vary within a given rock, the partitioning ratio is relatively constant. These ratios show that whereas some rocks have ‘quenched in’ the initial zirconium contents of the oxides, other rocks have reequilibrated to subsolidus temperatures as low as 850°C. The zirconium partitioning between coexisting ilmenite and ulvöspinel appears to be a sensitive indicator of differences in cooling histories of lunar rocks.

X-ray study and mössbauer spectroscopy on lunar ilmenites (Apollo 11)

A comparison of lunar ilmenites (Apollo 11, 10047, 13) with terrestrial ilmenites by means of electron microprobe analysis, X-ray and Mössbauer spectrometry showed that the lunar samples contained no Fe 3+ but excess Ti 3+. This causes an increase of the c-axis as compared with stoichiometric ilmenite.

Luna 16: An opaque mineral study and a systematic examination of compositional variations of spinels from Mare Fecunditatis

Opaque minerals identified by reflection microscopy and electron microprobe include ilmenite, members of the chromite-pichrochromite-hercynite-ulvospinel series, rutile, troilite, metallic iron and metallic nickel-iron alloys. Spinel compositions indicate an extensive but incomplete solid solution series between FeCr 2O 4-FeAl 2O 4 and Fe 2TiO 4. Members of this series are common to samples from each of the Apollo landing sites but the Luna 16 spinels are characterized by High Al (15–25% Al 2O 3), high Mg (4–9% MgO) contents, by compositions intermediate between (FeCr 2O 4-FeAl 2O 4)-Fe 2TiO 4 typical of Apollo 11, and by considerable variation of Cr/Al as a function of Fe/Mg not previously observed. The ratios Cr/Al and Fe/Mg show maximum variability in low-Ti chromites whereas intermediate titanian-chromites and chromian-ulvospinels show less variation of Cr/Al, and Fe/Mg is constant and high (⋍0.97). Ilmenite contains between 0.1 and 5.7 wt.% MgO; high geikielite contents and contrasting coexisting ilmenite textures (skeletal and phenocrystic) suggest possible reaction of early formed armalcolite with liquid. Shock deformation of ilmenite gives rise to simple lamellar twins in low intensity shocked fragments; complexly deformed twins and evidence of shock-induced melting are present in highly shocked fragments; and peripheral annealing of preexisting twin lamellae, associated with partial melting, is recorded for the first time in lunar ilmenite.

Mössbauer Spectroscopy of Moon Samples

Lunar bulk sample 10084,85 (< 1 mm size dust), and samples from rocks 10017,17 (fine grained, vesicular), 10046,17 (breccia), 10057,59 (fine grained, vesicular, top surface), 10057,60 (fine grained, vesicular, interior), and 10058,24 (medium grained, not vesicular) have been investigated by (57)Fe Mössbauer spectroscopy. Iron metal and the Fe(2+) minerals ilmenite, pyroxene, troilite, and iron containing glass have been identified. An iron line of sample 10084,85 (originally sealed in nitrogen) showed no significant intensity change when the sample was exposed to air. The antiferromagnetic transition in several lunar ilmenites at 57(0) +/- 2 degrees K corresponds to stoichiometric FeTiO,. Magneticallv separated 10057 showed troilite and somne metallic iron.