Brown powder or crystals from AAA batteries

Question for chemist Dopers:

I know the white crystalline stuff from leaking alkaline AAA batteries is usually potassium hydroxide or potassium carbonate, but what if it’s brown powdery or crystalline fluff instead of white that is spilling out the end of a battery?
Maybe potassium hydroxide or carbonate that’s been exposed to moisture in air for a long time?

Or something else entirely?

Wish I could attach a photo

the case is usually steel, so I’d suspect it’s rust. IIRC the manganese dioxide cathode material is almost black in color.

Thanks. Maybe the caustic stuff ate away the wall and then oxidized?

I keep seeing “Brain Powder…” in the thread title.
I am not smart enough to participate in this thread, but I really had to share that bit about brain powder. I promise I am also interested in the chemistry answers.

JZ is right its MnO2 its a really good oxidizer and can get violent once it ignites. I remember in the 90s when i got ahold of an Anarchist’s cookbook it had a section on how to harvest MnO2 from alkaline batteries to make thermite/flashbang/bomb. I remember I opened up one battery and quickly realized it was going to take alot of time and batteries to aquire enough for some fun. So i gave up and bought some firecrackers.