Acicular plessite is a
fine-grained mixture of kamacite and taenite, characterized by the needle-like
(acicular) shape of the kamacite crystals embedded within the taenite. This
distinctive texture emerges as iron meteorites cool slowly from temperatures
around 1,200°C. During this cooling, kamacite and taenite phases develop
within the retained taenite portion of the metal.
Acicular plessite is one of several plessite
varieties, alongside types such as granular, net, and comb plessite. It
specifically forms as "fields" within iron meteorites, arising from
the gradual cooling and phase transformation of taenite. As the temperature
decreases, kamacite separates out-or exsolves-from the taenite, creating a
finely interwoven structure of kamacite needles and residual taenite.
Classified as a secondary structure, acicular
plessite is commonly observed in octahedrites, occupying the spaces between the
kamacite and taenite lamellae. It is one of the several plessite types,
including Granular, Net, Comb, and others.
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