🔎 UNIDENTIFIED I am not sure what this rock is before it was broken was it was about the size of an egg.

[Krispy.io]

I found this weird looking tan/brown looking rock somewhere in the mountains in Montana and noticed it had this weird spiral hole in it a decided to break it open and the inside was black and dark brown
as well as powdered almost like mushroom spores

 

[Treasure_Hunter]

Looks like some kind of geode.

 

[crashbandicoot]

Petrified nut? I know I left myself open on that one.

 

[Red-Coat]

I think you found a concretion filled with iron oxides. The spiral 'opening' looks to be what's left of a gastropod shell and fossil fragments like that often act as the trigger for mineral precipitation or the nucleus around which concretions form.

 

[blauer]

It looks to be an ironstone cocreation. I found a few and they were used by native Americans as "paint pots" . I have pics somewhrere....

 

[GoldieLocks]

Could you turn the pieces over and take a photo of the outside of the rock like shape? It really looks to me so far is that the easiest solution is the most likely. It is a mushroom as far as I can see. It is also too bad the "screw" part isn't in tact to clearly see.