Ore Petrography, Mineralogical and Chemical Composition of New Iron Meteorite (Al-Sherqat Meteorite) from Iraq

The meteorite with a single total mass of 630 gm as a visible meteorite has fallen on 22 March 2021, at 10:00 a.m. in Al-Sherqat subdistrict within Salah Al-Din, northern Iraq; and therefore, was named Al-Sherqat meteorite by the authors. It is characterized by a uniform structure of coherent and medium degree of malleability. It is of a well-crystalline structure and not homogeneous in composition. The Al-Sherqat meteorite is composed of metallic phases of 7.6 gm/cm3 density exhibiting an oriented intergrowth of kamacite (α-FeNi) with taenite showing a Widmanstätten pattern on an etched polished section with the finest octahedrite kamacite bandwidth of less than 0.2 mm. It is composed of Fe (86.9 wt%), Ni (9.63 wt%), P (1.31 wt%), S (0.628 wt%), Ti (0.623 wt%), Co (0.446 wt%), Mo (0.146 wt%), Cr (0.103 wt%), Cu (0.141 wt%), V (300 ppm), Nb (220 ppm), W (53 ppm), Ag (50 ppm), Pb (30 ppm), Zn (20 ppm), Sb (16 ppm), Sn (10 ppm) and As (3 ppm). Al-Sherqat meteorite was structurally classified as an iron meteorite belongs to the plessitic group (Opl)) with octahedrite finest bands (less than 0.2 mm) of the kamacite lamellae. Kamacite platelets in Al-Sherqat meteorite are almost not a continuous plate network. Chemically, it belongs to the IIC type of magmatic group based on the amount of nickel (9.63%), where IIC is typically octahedrites has 9.3 – 11.5% Ni. The presence of kamacite, taenite, schreibersite, daubréelites, pentlandite, chromite, and wusite in Al-Sherqat meteorite are in accordance with IIC group of the iron meteorites. Al-Sherqat meteorite belongs to M-type considering a metallic core fragmented by impact asteroid. The most probable source of this meteorite is the core of an asteroid that melted early in its history.

Campo del Cielo – an Iron Meteorite found in Argentina

Fragments of the “Campo del Cielo” meteorite were first reported by conquistadores in Argentina in as early as 1576. This meteorite belongs to the group of iron meteorites and is classified as a group IA coarse octahedrite. The use of meteoric iron to make objects of daily use or hunting weapons in prehistoric times is only confirmed by very few finds. Metallographic examinations were performed to assess if it was realistic and in fact feasible to process meteoric iron. The bulk of the examined “Campo del Cielo” meteorite fragment found in Argentina is kamacite (α-Fe) with approx. 5.3 wt.% of dissolved Ni. Graphite was also detected in addition to various non-metallic phases. Due to high temperatures during processing, graphite can dissolve and a steel microstructure would form as a result.

57Fe Mössbauer Analysis of Meteorites and Tektites

This review presents studies on iron meteorites (Campo del Cielo fall and an unregistered iron meteorite), an unregistered stony meteorite from Northwest Africa, and 13 tektites from the American, European, and Australasian strewn fields. The main experimental technique used in the studies was Mössbauer spectroscopy, both in transmission and backscattering geometries. For the latter, a MIMOS II spectrometer was used. Additionally, optical and scanning electron microscopies and X-ray diffraction were used. In the studied iron meteorites, kamacite is found as the main mineral. Campo del Cielo meteorite exhibits Widmanstätten patterns and schreibersite inclusions. The unregistered iron meteorite has Neumann lines and schreibersite inclusions. We have assigned Campo del Cielo as an octahedrite and the unregistered iron meteorite as a hexahedrite. The unregistered stony meteorite is composed mainly of iron-free silicates; at 4.2 K, the spectrum indicates maghemite and 1% troilite. The Cambodian tektite appeared individualized from other australasites, unlike the moldavite, which tends to cluster with them. Our analyses do not allow dismissing doubts on the provenance of tibetanites. The Fe3+/Fe2+ ratio was found to be higher for Muong Nong-type tektites than for splash-form tektites, as expected from their morphology and solidification from melt at lower temperature.

Early volatile depletion on planetesimals inferred from C–S systematics of iron meteorite parent bodies

During the formation of terrestrial planets, volatile loss may occur through nebular processing, planetesimal differentiation, and planetary accretion. We investigate iron meteorites as an archive of volatile loss during planetesimal processing. The carbon contents of the parent bodies of magmatic iron meteorites are reconstructed by thermodynamic modeling. Calculated solid/molten alloy partitioning of C increases greatly with liquid S concentration, and inferred parent body C concentrations range from 0.0004 to 0.11 wt%. Parent bodies fall into two compositional clusters characterized by cores with medium and low C/S. Both of these require significant planetesimal degassing, as metamorphic devolatilization on chondrite-like precursors is insufficient to account for their C depletions. Planetesimal core formation models, ranging from closed-system extraction to degassing of a wholly molten body, show that significant open-system silicate melting and volatile loss are required to match medium and low C/S parent body core compositions. Greater depletion in C relative to S is the hallmark of silicate degassing, indicating that parent body core compositions record processes that affect composite silicate/iron planetesimals. Degassing of bare cores stripped of their silicate mantles would deplete S with negligible C loss and could not account for inferred parent body core compositions. Devolatilization during small-body differentiation is thus a key process in shaping the volatile inventory of terrestrial planets derived from planetesimals and planetary embryos.

A 4,565-My-old andesite from an extinct chondritic protoplanet

The age of iron meteorites implies that accretion of protoplanets began during the first millions of years of the solar system. Due to the heat generated by 26Al decay, many early protoplanets were fully differentiated with an igneous crust produced during the cooling of a magma ocean and the segregation at depth of a metallic core. The formation and nature of the primordial crust generated during the early stages of melting is poorly understood, due in part to the scarcity of available samples. The newly discovered meteorite Erg Chech 002 (EC 002) originates from one such primitive igneous crust and has an andesite bulk composition. It derives from the partial melting of a noncarbonaceous chondritic reservoir, with no depletion in alkalis relative to the Sun’s photosphere and at a high degree of melting of around 25%. Moreover, EC 002 is, to date, the oldest known piece of an igneous crust with a 26Al-26Mg crystallization age of 4,565.0 million years (My). Partial melting took place at 1,220 °C up to several hundred kyr before, implying an accretion of the EC 002 parent body ca. 4,566 My ago. Protoplanets covered by andesitic crusts were probably frequent. However, no asteroid shares the spectral features of EC 002, indicating that almost all of these bodies have disappeared, either because they went on to form the building blocks of larger bodies or planets or were simply destroyed.

Half of Earth’s Nitrogen May Be Homegrown

A new analysis of iron meteorites reveals a distinct isotopic signature that suggests nitrogen was present around early Earth.