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Perhaps some kind of corrosion.
This material consists of ferrite.
Ferrite contains iron.
Most likely on the surface is Iron oxide Fe2O3.
This could have happened due to prolonged exposure to water.
It can be cleaned with gasoline.
It doesn’t affect to the quality of the ferrite.
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Hello @2881406921,
Thank you for posting to the DigiKey forum.
The part looks like it is in good condition. For inductors, there is a protective coating that can sometimes appear speckled from the epoxy or resin.
Mold has a different texture. I would suggest looking under a microscope to see if it is fuzzy or raised. The coating should be smooth. You can also use some isopropyl alcohol and clean off the surface. Mold may come off with a gentle cleaning, while a coating will not be affected.
Thank you,
Victoria
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