Construct · 1 fields · 4 citations

Widmanstatten pattern: a standalone construct

One name. One construct. A landmark on the map.

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Widmanstattenpattern1 CONSTRUCTWidmanstätten fig.THOMSON · IRON FIGURE

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Meteoritics and metallography

The interleaved crystal figure etched from iron meteorites

William Thomson first produced the figure in 1804, treating a slice of the Krasnojarsk pallasite (a stony-iron meteorite found in Siberia) with nitric acid and observing the geometric bands the acid brought out; Alois von Widmanstätten reached the same result independently in Vienna in 1808 by heating polished meteoritic iron, and Carl von Schreibers named the figures after him in 1820, the name that stuck. The pattern is a set of interleaved bands of two iron-nickel alloys, kamacite (the low-nickel phase) and taenite (the high-nickel phase), that grew along the octahedral planes of a single parent crystal as the metal slowly cooled, and it becomes visible when a cut face is polished and etched because the two alloys resist the acid differently. It occurs in the class of iron meteorites called octahedrites and is absent from ordinary terrestrial iron. What makes it a landmark is that it records extremely slow cooling: the bands form only over millions of years, at rates on the order of a few degrees per million years inside the metallic core of an asteroid, so the figure is read as a record of an origin no furnace can reproduce, and the width of its kamacite bands is used both to classify octahedrites and to estimate how fast the parent body cooled.[1][2][3][4]

Unit
A crystallographic microstructure of iron-nickel meteoritic metal, the interleaved kamacite and taenite bands, gauged by kamacite band width (conventionally in millimetres)
Recovery means
Not applicable
Measured by
Revealed on a cut, polished section etched with dilute nitric acid (nital); band orientation and kamacite band width are read under optical or electron microscopy to classify the meteorite and infer its cooling rate

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Nearby constructs

crystal4 fields · 4 citationsjingle · one word, four constructscrystallization4 fields · 6 citationsjingle · one word, four constructsetching3 fields · 4 citationsjingle · one word, three constructs

References

  1. Thomson, G. (1804). Essai sur le fer malléable trouvé en Sibérie par le Prof. Pallas. Bibliothèque Britannique, 27, 135–154.
  2. Paneth, F. A. (1960). The discovery and earliest reproductions of the Widmanstätten figures. Geochimica et Cosmochimica Acta, 18(3–4), 176–182. https://doi.org/10.1016/0016-7037(60)90085-5
  3. Yang, J., & Goldstein, J. I. (2005). The formation of the Widmanstätten structure in meteorites. Meteoritics & Planetary Science, 40(2), 239–253. https://doi.org/10.1111/j.1945-5100.2005.tb00378.x
  4. Goldstein, J. I., Scott, E. R. D., & Chabot, N. L. (2009). Iron meteorites: Crystallization, thermal history, parent bodies, and origin. Chemie der Erde - Geochemistry, 69(4), 293–325. https://doi.org/10.1016/j.chemer.2009.01.002

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