Muonionalusta Iron Meteorite Slice, IVA Fine Octahedrite, 292.00g, Etched Widmanstätten Pattern

Etched crystal structure from an asteroid core

This 292.00g Muonionalusta slice displays the characteristic Widmanstätten pattern of an IVA fine octahedrite through chemical etching that reveals the internal nickel-iron crystal structure. The parallel kamacite lamellae intersect at consistent angles, creating geometric bands that formed during slow cooling in the metallic core of a differentiated asteroid over millions of years. The etching process dissolves kamacite at a faster rate than taenite, producing visible relief and contrast across the polished surface.

The slice measures substantial enough for display while maintaining clarity across the entire etched face. The pattern remains continuous from edge to edge, showing no significant oxidation or surface weathering that would obscure the crystallographic features. This specimen originated from material recovered in northern Sweden beginning in 1906, giving it both scientific classification and established provenance within the meteorite community.

Kamacite lamellae and crystallographic orientation

The Widmanstätten pattern visible on this slice represents the three-dimensional arrangement of kamacite plates within a taenite matrix, a structure that forms only under conditions of extremely slow cooling in space. The bandwidth, or spacing between kamacite lamellae, classifies Muonionalusta as a fine octahedrite with measurements typically between 0.5 and 1.0 millimeters. This narrow spacing produces a tightly woven pattern with high visual density.

Etching with dilute acid preferentially attacks the kamacite phase, leaving taenite bands raised in relief. The resulting pattern follows the cubic crystal structure of the parent metal, with lamellae oriented along specific crystallographic planes. The angles where these bands intersect reflect the octahedral symmetry of the original crystal lattice, a feature that remains consistent across all properly oriented sections of the same meteorite.

Formation in a differentiated asteroid

IVA iron meteorites formed in the molten metallic core of a planetary body that underwent complete differentiation early in solar system history. As the core cooled at rates measured in degrees per million years, nickel and iron atoms migrated through the melt and crystallized into the ordered structure now visible in this slice. The slow cooling rate allowed large crystals to form and kamacite to exsolve from taenite along preferred crystallographic directions.

Catastrophic collisions later fragmented the parent body, exposing core material to space and eventually delivering it to Earth as iron meteorite falls and finds. Muonionalusta represents one of these core fragments, offering direct evidence of planetary-scale melting, differentiation, and metal crystallization that occurred more than 4.5 billion years ago. For additional information on meteorite formation and identification, see Learn About Meteorites.

The story

The first piece of Muonionalusta was found in 1906 in the forests of Swedish Lapland, about 140 km north of the Arctic Circle. According to the locality record, it was a 10-year-old boy tending cattle in the forest about 3 km southwest of the village of Kitkiöjärvi who came across the heavy iron mass. The geologist A. G. Högbom described it in 1909, and it takes its name from Muonionalusta, a place on the Muonio River along the border between Sweden and Finland.

For most of the twentieth century the finds came slowly: only four masses, of 6 to 15 kg, had turned up by chance by 1989. Searching with metal detectors since then has recovered many more, buried in glacial till from the surface to at least 4 m down, ranging from 40 g to 1.2 tonnes.

They lie in glacial till because they have been on Earth a very long time. Holtstam and colleagues cite a terrestrial age of more than 800,000 years, measured from cosmogenic beryllium-10 and chlorine-36, meaning the pieces have lived through at least four major glaciations since they landed.

Sources: Holtstam et al. (2003), cited below; Mindat locality record for Muonionalusta; The Muonionalusta iron meteorites from Lapland, Sweden: New finds and findings.

What the research reports

The Meteoritical Bulletin classifies Muonionalusta as Iron, IVA. Its classification history begins as “Iron-fine octahedrite” in Meteoritical Bulletin 20 (1961), with the IVA group assigned in the Natural History Museum Catalogue of Meteorites (2000) and in MetBase (2006). The entry records a find year of 1906 in Sweden and a mass of 230 kg, a figure from the early finds; searches since then have recovered far more material. The studies below come from the authors’ own samples and methods, and are given here as the studies state them.

Holtstam et al. (2003): stishovite in an iron meteorite

D. Holtstam, C. Broman, J. Söderhielm and A. Zetterqvist published First discovery of stishovite in an iron meteorite (Meteoritics & Planetary Science, volume 38, pages 1579 to 1583, 2003). Stishovite is a very high-pressure form of silica, and Muonionalusta was the first iron meteorite in which it had ever been found.

Blichert-Toft et al. (2010): an early age for the IVA core

J. Blichert-Toft, F. Moynier, C.-T. A. Lee, P. Telouk and F. Albarède published The early formation of the IVA iron meteorite parent body (Earth and Planetary Science Letters, volume 296, pages 469 to 480, 2010). Lead isotopes in the troilite inclusions of Muonionalusta gave an age of 4,565.3 ± 0.1 million years, placing the solidification of the IVA parent body’s core within a few million years of the first solids in the solar system. The authors write that the stishovite shows the meteorite was “heavily shocked,” possibly during the breakup of the parent body about 400 million years ago.

Brennecka et al. (2018): a caveat on that age

A later study led by G. A. Brennecka, Uranium isotope ratios of Muonionalusta troilite and complications for the absolute age of the IVA iron meteorite core (Earth and Planetary Science Letters, 2018), measured the uranium isotope ratio in Muonionalusta troilite directly. The 2010 age relied on an assumed uranium isotope ratio, and as the title says, the new measurements complicate the absolute age, so the 4,565.3 million year figure is best read with that caveat.

Frequently asked questions

Is this meteorite authenticated? Muonionalusta is classified in the Meteoritical Bulletin as an IVA fine octahedrite from Sweden. You can verify this classification through the official Meteoritical Bulletin database. This specimen includes a certificate of authenticity documenting its classification and provenance.

What does the Widmanstätten pattern show? The Widmanstätten pattern is the visible expression of kamacite and taenite crystal orientations that developed during slow cooling in an asteroid core. The geometric bands represent kamacite plates that crystallized along octahedral planes in the original metal lattice. This structure forms only in meteoritic iron-nickel alloys and cannot be reproduced artificially under terrestrial conditions.

What is included with this specimen? This listing includes the 292.00g etched Muonionalusta slice and a certificate of authenticity. No display stand is included unless specifically noted.

How is the slice prepared? The slice has been cut, polished to a smooth surface, and chemically etched with dilute acid to reveal the internal crystal structure. Etching dissolves kamacite preferentially, creating relief between the kamacite and taenite phases that makes the Widmanstätten pattern visible to the eye.

Why is Muonionalusta significant to collectors? Muonionalusta combines clear IVA classification, a well-defined Widmanstätten pattern with fine bandwidth, and documented Swedish provenance dating to 1906. The etched pattern provides both visual appeal and direct evidence of crystallization processes in asteroid cores, making it scientifically and aesthetically valuable to collectors.

How do I verify this is the same specimen shown in these photographs?
This stone is recorded under serial TC-00024. Its specimen record is a permanent page holding the classification data as published in the Meteoritical Bulletin, the recorded weight, and photographs of this exact stone. Meteorite surfaces, cut faces and clast patterns are individual to each stone, so a specimen in hand can be compared against those photographs and weighed against the recorded figure.

Display and collection value

Etched iron meteorite slices serve as both display pieces and scientific specimens. The Widmanstätten pattern remains stable under normal indoor conditions, though light surface oxidation may develop over years of exposure to humidity. Collectors typically store iron meteorites in low-humidity environments or apply protective coatings to preserve the etched surface contrast.

This 292.00g slice provides sufficient size for clear pattern visibility while remaining practical for desktop or cabinet display. The continuous pattern from edge to edge and the absence of significant weathering give this specimen strong presentation quality. Muonionalusta's recognition within the collector community and its confirmed classification make it suitable for both new and established collections. View additional classified specimens in our Iron Meteorites collection.

Meteoritical Bulletin entry: Muonionalusta | Classification: Iron meteorite (IVA fine octahedrite) | Find, Sweden, 1906

Specimen record

This specimen is serialized as TC-00024 and is issued with a certificate card bearing that serial. The serial indexes a permanent public record maintained by Treasure Coast Meteorite Co., and every issued serial is listed in the Specimen Registry.