The Gressk meteorite, like many
iron meteorites, contains rhabdites--needle-like or plate-like inclusions of
schreibersite, a phosphide mineral (Fe,Ni)3P.
First-generation rhabdites form during the primary
cooling phase as the meteorite solidifies from its molten state. The larger
size (1-3 mm plates) and even distribution suggest they had ample time to
nucleate and grow in a relatively stable, slow-cooling environment, likely deep
within a planetary body's core or mantle. This is typical of meteorites that
cooled over millions of years in space after their parent body
differentiated.
Second-generation rhabdites are smaller
inclusions (8-10 µm) that emerge later, during thermal metamorphism caused
by reheating events-possibly from impacts or proximity to heat sources like the
Sun. The reheating mobilizes elements like phosphorus and nickel, allowing new,
smaller schreibersite crystals to nucleate, often along grain boundaries or in
localized zones.
This dual-generation pattern of initial formation
under slow, controlled cooling, followed by a more chaotic history of impacts
or thermal events that altered its structure, details significant events in the
meteorite's history.
|
