Neumann lines

Abstract: A slab of the Willamette ungrouped iron contains elongated troilite nodules (up to ~2 × 10 cm) that were crushed and penetrated by wedges of crushed metal during a major impact event. What makes this sample unique is the contrast between the large amount of shock damage and the very small (~1%) amounts of shock melting in the large troilite nodules. The postshock temperature was low, probably ≾960 °C. The Widmanstatten pattern has been largely obscured by an episode of postshock annealing that caused recrystallization of the kamacite. The shock and thermal history of Willamette includes (1) initial crystallization and formation of multicentimeter-size troilite nodules from trapped melt, (2) impact-induced melting of metal-sulfide assemblages to form lobate taenite masses a few hundred micrometers in size, (3) impact-crushing of the nodules and jamming of metal wedges into them, (4) simultaneous crushing of metal grains adjacent to sulfide throughout the meteorite, (5) postshock annealing causing minor recrystallization of metal and troilite, and (6) a late-stage shock event (and additional annealing) producing Neumann lines in the kamacite.

Abstract: In the third century AD, replicas of small denomination coins were manufactured in the border areas of the Roman Empire. They are composed of an iron core with a non-ferrous metal layer and are called “Subferrati”. Four roman coins, one of them from Loig, two of them from Enns, and one of them from Magdalensberg, were metallographically prepared and examined in the LOM, SEM-BSE, and by means of XRF. The non-ferrous metal layers are composed of lead-containing bronzes with segregation structures from a α-copper solid solution, Sn-rich δ-phase, and Pb. Spherically shaped iron inclusions could also be observed in the bronze coating. They can be attributed to the fact that the iron core was dipped in liquid bronze. The coins' iron cores mainly contain ferrite and little pearlite. Elongated inclusions originate from the iron manufacture in the bloomery furnace and subsequent forging. The Neumann lines are in the ferrite formed during minting. Copper could also be observed on the ferrite grain boundari...

Abstract: Some of the macroscopic and microscopic features which are encountered in iron meteorites can be ascribed to mechanical deformation. Relatively mild deformation within the meteorite parent body before the kamacite has begun to precipitate may produce macroscopic twins which are subsequently decorated by the precipitation of kamacite. In addition, the stresses which arise by virtue of the volume changes during the precipitation of kamacite may produce transformation twins on a microscopic scale within the kamacite. These transformation twins appear similar to partially annealed Neumann lines and are decorated by the subsequent precipitation of rhabdite. Decorated transformation twins are usually accompanied by a later generation of fresh or undecorated Neumann lines. More violent deformation effects may arise when the original meteorite parent bodies are fragmented, and also when subsequent collisions occur between fragments in space. Similar eifects may sometimes be produced by particularly violent impact with the earth, but a satisfactory distinction can be made between pre-terrestrial damage and damage during earth residence, if the heat alteration zone which is produced during atmospheric entry can be shown to be of later origin than the mechanical deformation.

Abstract: 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 Mossbauer 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 Widmanstatten 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.