This is #50, the last topic (for now) of this
visual presentation of Primary and Secondary structures - Meteorites (mostly
iron structures).
The Bella Roca IIIAB meteorite is an example of
both its initial formation and the dramatic changes it underwent later. Likely
born in the core of a differentiated asteroid, it emerged from the slow cooling
and solidification of molten iron-nickel metal in the early solar system. This
process created its primary minerals: taenite (rich in nickel) and kamacite
(nickel-poor), their patterns shaped by cooling rates and nickel levels.
Between these, plessite-a delicate blend of taenite and kamacite-forms
intricate "fields." As cooling continued, phosphorus concentrated in
the leftover melt, giving rise to schreibersite, an iron-nickel phosphide that
adds another layer to its composition.
The meteorite's secondary features reveal a
history of violent space collisions. Shock events reshaped and hardened the
kamacite grains, while rapid cooling of taenite during these impacts formed
martensite, a brittle phase nestled within plessite zones. Extreme pressure and
heat from these collisions also turned kamacite into a hatched ?-phase
(epsilon-phase iron), a high-pressure structure dotted with schreibersite
residues (phosphides)-tiny remnants likely deposited during slow cooling after
the shocks. These events also shuffled elements around, forming phosphorus-rich
pockets and precipitates, further marking Bella Roca's chaotic past.
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