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On the night of March 26, 2003, a large meteorite broke up and fell upon the south suburbs of Chicago. The name Park Forest, for the village that is at the center of the strewnfield, has been approved by the nomenclature committee of the Meteoritical Society. Satellite data indicate that the bolide traveled from the southwest toward the northeast. The strewnfield has a southeast-northwest trend; however, this is probably due to the effects of strong westerly winds at high altitudes. Its very low 56Co and very high 60Co activities indicate that Park Forest had a preatmospheric mass that was at least ~900 kg and could have been as large as ~7 x 10^3 kg, of which only ~30 kg have been recovered. The average compositions of olivine and low-Ca pyroxene, Fa24.7 ± 1.1 and Fs20.8 ± 0.7, respectively, and its bulk oxygen isotopic composition, δ18O = +4.68‰, δ17O = +3.44‰, show that Park Forest is an L chondrite. The ferromagnesian minerals are well equilibrated, chondrules are easily recognized, and maskelynite is mostly ≤50 μm across. Based on these observations, we classify Park Forest as type 5. The meteorite has been strongly shocked, and based on the presence of maskelynite, mosaicism and planar deformation features in olivine, undulatory extinction in pyroxene, and glassy veins, the shock stage is S5. The meteorite is a monomict breccia, consisting of light-colored, angular to rounded clasts in a very dark host. The light and dark lithologies have essentially identical mineral and oxygen isotopic compositions. Their striking difference in appearance is due to the presence of a fine, pervasive network of sulfide veins in the dark lithology, resulting in very short optical path lengths. The dark lithology probably formed from the light lithology in an impact that formed a sulfide-rich melt and injected it into cracks.

An ordinary chondrite fall in southeast Michigan, USA (near the crossroads hamlet of Worden in northeast Washtenaw County) penetrated the garage roof of a private home on 1997 September 1. The Worden chondrite comprises silicate matrix, mineral fragments, chondrules, chondrule fragments, and opaque primary phases. Electron microprobe analyses (olivine, Fa23.9; orthopyroxene, FS20.1, En78.8, W01) indicate diagnostic L-chondrite silicate mineral compositions. Recognizable chondrules and chondrule fragments constitute up to 42 vol%. Chondrule boundaries are readily discernable (especially where chondrules have rims of opaque material) but not sharp, and discrete plagioclase crystals are visible in the devitrified mesostasis of barred olivine chondrules; together, these characteristics suggest petrologic type S. The spatially averaged ensemble of shockrelated features (optical extinction of olivine grains, minor localized shock melt) suggests assignment of a shock stage of S3. The 26 Al and 22Na activities are typical for an L chondrite. Worden fell near the most recent solar minimum in 1997, and the 22Na production rate should have been at a level approaching the maximum levels due to solar modulation of the galactic cosmic-ray flux. The low value for the Worden 22Na activity relative to those observed in chondrite falls associated with the 1969 solar maximum and 1976 solar minimum suggests a relatively small preatmospheric size. The 60Co activity confirms the indication of a small body. The 56Co activity was essentially zero, indicating that none of the recovered meteorite contained material exposed to solar cosmic rays. The Worden chondrite is the fourth documented fall in Michigan, and the fourth stony meteorite recovered in Michigan; all other Michigan meteorites are finds, not observed falls, and are iron meteorites. All Michigan falls to date are ordinary chondrites. The three falls prior to Worden were Allegan (HS) fell 1899; Rose City (HS, brecciated, black (dark matrix)) fell 1921 ; and Coleman (L6, veined (shocked); Osborn et aI., 1997) fell 1994. Worden has a much lighter matrix than Rose City, and is less extensively thermally and shock metamorphosed than either Rose City (StOffler et aI., 1991) or Coleman.

— The compositionally typical H5 chondrite St-Robert has an exposure age, 7.8 Ma, indistinguishable from that of the main cluster of H chondrites. Small values of the cosmogenic 22Ne/21Ne ratio in interior samples imply a pre-atmospheric radius on the order of 40 cm. Sample depths based on tracks and the production rates of Bhattacharya et al. (1973) range from 6 to ∼40 cm and are generally larger than depths estimated from published 60Co activities, perhaps because the track production rates adopted are too high. Depth profiles of the production rates of 14C, 36Cl, 26Al, 10Be, and 21Ne in stony material show increases with depth and reach levels 5% to 15% higher than expected from modeling calculations. The maximum concentrations in St-Robert are, however, generally comparable to those measured for the L5 chondrite, Knyahinya, whose pre-atmospheric radius of ∼45 cm is thought to lead to the maximum possible production rates in chondrites. We infer that the pre-atmospheric radius of St-Robert was within 5 cm of the value that supports maximum production rates (i.e., 45 ± 5 cm). This radius corresponds to a pre-atmospheric mass of (1.3 ± 0.4) × 103 kg. The agreement of exposure ages for St-Robert obtained in several different ways and the similarity of the depth profiles for 14C, 26Al, 10Be, and 21Ne argue against a lengthy pre-exposure of St-Robert on the parent body and against a two-stage exposure after launch from the parent body. Following Morbidelli and Gladman (1998), we suggest that St-Robert was chipped from deep in its parent body, spent the next 7–8 Ma without undergoing a major collision, was nudged gradually into an orbital resonance with Jupiter, and then traveled quickly to Earth.

— A 0.5 kg stony meteorite associated with a bright bolide seen over southeastern Michigan on 1994 October 20 has been recovered. The circumstances of the fall and recovery of this chondrite, named Coleman, are presented. The most likely trajectory from the observations of the event implies preatmospheric orbital parameters typical of meteorites. Gamma-ray spectrometry of the cosmogenic radionuclides showed that the recovered mass was an interior fragment of a larger body and revealed abnormally high 22Na and 26Al activity. Electron microprobe analysis yielded compositions of Fa24.1 and Fs20.3, which are consistent with an L-chondrite classification. Petrographically, the presence of chondrules, the observed mineralogy and the degree of chondrule-matrix integration suggests assignment to petrologic type 6.

The St-Robert (Quebec, Canada) meteorite shower occurred on 1994 June 15 at 0h02m UT accompanied by detonations audible for >200 km from the fireball endpoint. The fireball was recorded by visual observers in Vermont, New York State, New Hampshire, Quebec and Ontario as well as by optical and infrared sensors in Earth-orbit. Penetration to an altitude of 36 km occurred ∼60 km to the northeast of Montreal, where the bolide experienced several episodes of fragmentation. A total of 20 fragments of this H5 chondrite, comprising a total mass of 25.4 kg, were recovered in an ellipse measuring 8 × 3.5 km. One fragment of the shower partially penetrated the aluminum roof of a shed. Interpretation of the visual and satellite data suggests that the fireball traveled from south-southwest to north-northeast, with a slope from the horizontal of 55°–61°. A statistical evaluation of the likely heliocentric orbits for the body prior to collision with the Earth, coupled with theoretical modeling of the entry, suggests an entry velocity in the range of 12.7–13.3 km/s; the meteoroid had moved in a low-inclination orbit, with orbital perihelion located extremely close to the Earth's orbit. From satellite optical data, it is found that the photometric mass consumed during the largest detonation is ∼1200 kg. Estimation of the amplitude of the acoustic signal detected by the most distant observer yields a source energy near 0.5 kt TNT equivalent energy, which corresponds to a mass of order 10 metric tonnes. This measure is uncertain to approximately one order of magnitude. Theoretical modeling of the entry of the object suggests a mass near 1600 kg. Cosmogenic radionuclide activities constrain the lower initial mass to be ∼700 kg with an upper limit near 4000 kg. Seismic data possibly associated with the fireball suggest extremely poor coupling between the airwave and the ground. The total mass estimated to have reached the ground is ∼100 kg (in material comprising >55 g fragments), while the preatmospheric mass is found to be most probably in the range of 1200–2000 kg.

We describe a previously unreported meteorite found in Axtell, Texas, in 1943. Based on the mineralogical composition and texture of its matrix and the sizes and abundance of chondrules, we classify it as a CV3 carbonaceous chondrite. The dominant opaque phase in the chondrules is magnetite, and that in refractory inclusions is Ni-rich metal (awaruite). Axtell, therefore, belongs to the oxidized subgroup of CV3 chondrites, although unlike Allende it escaped strong sulfidation. The meteorite bears a strong textural resemblance to Allende, and its chondrule population and matrix appear to be quite similar to those of Allende, but its refractory inclusions, thermoluminescence properties, and cosmogenic Co-60 abundances are not. Our data are consistent with a terrestrial age for Axtell of approximately 100 years and a metamorphic grade slightly lower than that of Allende.

The Noblesville meteorite is a genomict, regolith breccia (H6 clasts in H4 matrix). Moessbauer analysis confirms that Noblesville is unusually fresh, not surprising in view of its recovery immediately after its fall. It resembles 'normal' H4-6 chondrites in its chemical composition and induced thermoluminescence (TL) levels. Thus, at least in its contents of volatile trace elements, Noblesville differs from other H chondrite, class A regolith breccias. Noblesville's small pre-atmospheric mass and fall near solar maximum and/or its peculiar orbit (with perihelion less than 0.8 AU as shown by natural TL intensity) may partly explain its levels of cosmogenic radionuclides. Its cosmic ray exposure age of about 44 Ma is long, is equalled or exceeded by less than 3 percent of all H chondrites, and also differs from the 33 +/- 3 Ma mean exposure age peak of other H chondrite regolith breccias. While Noblesville is now among the chondritic regolithic breccias richest in solar gases, elemental ratios indicate some loss, especially of He, perhaps by impacts in the regolith that heated individual grains. While general shock-loading levels in Noblesville did not exceed 4 GPa, individual clasts record shock levels of 5-10 GPa, doubtless acquired prior to lithification of the whole-rock meteoroid.

[1] Reported Xe isotopic abundances in enstatite chondrites (EC's) show some variability, and this makes comparisons to other solar system reservoirs rather difficult. In contrast, we find uniform Xe isotopic abundances in the EC chondrite Abee for a variety of clasts, except for 128Xe and 129Xe, the isotopes affected by neutron capture in I and by extinct 129I. We report averages for the studied clasts which are consistent within error limits with OC-Xe and with the Q-Xe signature. On the other hand, the elemental abundance ratios Ar/Xe are variable between clasts. A strongly reducing environment which is indicated for enstatite meteorites was generally assumed to be consistent with conditions existing in the early inner solar system. Xe isotopic abundances in SNC meteorites from Mars and also those in some terrestrial wells show that distinct isotopic reservoirs coexisted on the same planets. In particular, the Xe isotopic signatures in terrestrial well gases show the presence of a minor distinct component in two of the reported four well gases. These authors suggested that the extra component represents solar Xe, but we show that also a meteoritic xenon reservoir of the Abee-Xe structure is an option. The reported Xe data in Ar-rich (subsolar) EC's show isotopic abundances slightly lighter than those in Abee-Xe, but the relative abundances of Ar, Kr, and Xe indicate only a minor component of elementally unfractionated solar Xe. The elemental ratios suggest rather a different origin for these gases: the loading of solar particles into grain surfaces during exposure at elevated temperatures during accretion of matter in the inner solar system. A model of this type was suggested for the accretion of gases now observed in the atmosphere on Venus. We note that disks of crystalline silicates (including enstatite and olivine) have been observed in T Tauri stars during their early evolution.

The preatmospheric mass of the Tagish Lake meteoroid was about 200,000 kilograms. Its calculated orbit indicates affinity to the Apollo asteroids with a semimajor axis in the middle of the asteroid belt, consistent with a linkage to low-albedo C, D, and P type asteroids. The mineralogy, oxygen isotope, and bulk chemical composition of recovered samples of the Tagish Lake meteorite are intermediate between CM and CI meteorites. These data suggest that the Tagish Lake meteorite may be one of the most primitive solar system materials yet studied.

Primitive meteorites contain up to 400 ppm of a very fine-grained type of carbon tentatively called C-delta. Evidence is presented here that part of all of the C-delta is primary, not shock-produced, diamond formed by stellar condensation as a metastable phase. It appears that interstellar dust contains diamond.