| Cloudy taenite is a high-nickel (Ni), secondary structure found in
iron meteorites, distinguished by its unique appearance and composition. It
emerges after the initial crystallization of primary metallic phases, forming
through the gradual diffusion of nickel and iron atoms. This slow process
creates fine intergrowths of taenite with another Ni-rich phase, often
tetrataenite (containing 49% to 57% Ni, sometimes referred to as
"clear" taenite). The result is a submicroscopic, two-phase mixture
that gives cloudy taenite its characteristic "cloudy" texture,
typically with a nickel content of 30% to 40%.
Taenite
rims, enriched in high-Ni tetrataenite, can also develop around existing
structures like kamacite lamellae or plessite fields. These rims form through
nucleation and growth during the slow cooling of the meteorite, driven by the
differing stabilities of iron-nickel phases at various temperatures. In
prepared specimens, such as those of the Grant meteorite, these rims often
appear as bright metallic borders encircling plessitic fields and kamacite,
highlighting the presence of tetrataenite.
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