Muonionalusta Iron Meteorite Slice, IVA Fine Octahedrite, 245.82g, Etched Widmanstätten Pattern

Etched crystalline structure from an asteroid core

This 245.82g Muonionalusta slice displays the geometrically ordered Widmanstatten pattern characteristic of IVA fine octahedrites. The etched surface reveals parallel kamacite and taenite lamellae that intersected during extremely slow cooling in the metallic core of a differentiated asteroid over 4.5 billion years ago. The pattern's clarity across this slice provides direct visual access to the internal crystalline architecture of extraterrestrial metal.

The specimen's weight and surface area allow the full Widmanstatten geometry to develop across multiple crystal orientations. Etching has brought the structural contrast into sharp relief, defining the boundaries between adjacent crystal planes and highlighting the angular intersections that define octahedral symmetry. This slice preserves the metallurgical record of core formation in a body that differentiated early in solar system history.

Kamacite and taenite crystallization

The Widmanstatten pattern forms when molten nickel-iron alloy cools over millions of years in the zero-gravity environment of an asteroid's interior. Kamacite, the low-nickel phase, crystallizes along octahedral planes within the parent taenite structure. The resulting intergrowth produces geometric lamellae that intersect at consistent angles across the metallic matrix.

Etching with dilute acid preferentially attacks kamacite, which recedes slightly relative to taenite. This differential response creates the three-dimensional relief visible on this slice. The pattern's consistency across the entire surface confirms that this material cooled as a single unified metallic body before fragmentation. Localized inclusions and minor surface texture variations document the specimen's terrestrial residence since recovery in 1906.

Core fragments from planetary differentiation

IVA iron meteorites represent material from the metallic core of a parent body that underwent complete differentiation during the first few million years of the solar system. Heating from short-lived radioactive isotopes melted the interior, allowing dense iron-nickel alloy to sink toward the center while silicate minerals migrated outward to form a mantle and crust. Subsequent catastrophic collisions exposed the core and ejected fragments into space.

Muonionalusta's crystalline structure records cooling rates of only a few degrees per million years, consistent with burial deep within a body at least tens of kilometers in radius. The IVA group is chemically and structurally distinct from other iron meteorite classes, indicating it originated from a separate parent body with its own differentiation history. This specimen provides physical evidence of planetary-scale processes that operated during the earliest stages of terrestrial planet formation. For broader context on meteorite origins and identification, see Learn About Meteorites.

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 Meteoritical Bulletin Database. This specimen includes a certificate of authenticity documenting its classification, weight, and provenance.

What does fine octahedrite mean? Fine octahedrite refers to the bandwidth of the kamacite lamellae in the Widmanstatten pattern. In fine octahedrites, kamacite bands measure between 0.5 and 1.0 millimeters in width. This places Muonionalusta in a specific structural category that reflects its cooling rate and nickel content, distinguishing it from coarse, medium, and finest octahedrites.

What is included with this specimen? You receive the 245.82g etched slice and a certificate of authenticity. No display stand is included unless separately confirmed.

How was the Widmanstatten pattern revealed? The slice was cut from bulk Muonionalusta material, then ground flat and polished to a mirror finish. Etching with dilute ferric chloride or nitric acid solution preferentially attacks the kamacite phase, causing it to recede relative to taenite. This differential etching produces the raised geometric pattern visible on the surface.

Display-grade iron meteorite for collectors

Muonionalusta remains one of the most visually distinctive iron meteorites available to collectors. The combination of strong pattern clarity, well-documented classification, and Swedish provenance makes it a foundational specimen for collections focused on iron meteorites or planetary differentiation. This 245.82g slice offers sufficient surface area to display the full geometric complexity of the Widmanstatten structure while remaining practical for cabinet or desk display.

The etched finish provides immediate visual impact and eliminates the need for additional surface preparation. Collectors seeking classified extraterrestrial metal with scientifically significant structure will find this specimen suitable for both display and study. For additional iron meteorite specimens with varied structures and classifications, explore our full Iron Meteorites collection.

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