Plessite
A fine-grained intergrowth of kamacite and taenite that fills the spaces in the Widmanstätten pattern.
Key facts
- Formula
- Kamacite and taenite intergrown
- Family
- Metals and alloys
- Crystal system
- A mixture of two minerals
What it is
Plessite is not a single mineral but a texture: a mixture of kamacite and taenite in grains too fine to see without magnification. It forms in the triangular and polygonal spaces between the large kamacite bands, where taenite stayed until low temperatures and then broke down into fine intergrowths. Its name comes from the Greek for filling.
Where it is found
It occurs in almost all octahedrites and in metal grains of ordinary chondrites. Its textures vary widely: comb-like, net-like, spotty or martensite-rich, depending on the nickel content and cooling history.
How it is recognised
On an etched slice, plessite fields appear as dark grey or patterned patches framed by bright taenite rims. Under magnification they show fine stripes or speckles.
Did you know?
Some iron meteorites have so much plessite that they are called plessitic octahedrites.
The variety of plessite textures has been classified into more than a dozen types.