Request ID of 'abnormality' in piece of slate

[Stimon]

Amateur with regards to stones and fossils but always interested me since I was little. Got this collection of stones an aunt assembled on here journeys. My jongest still picks up stones wherever he goes so I guess it runs in the family. He was actually looking in that same collection and broke what I believe is slate and found something with a distinct shape and different colour. Could this be a fossil or formation of other type of mineral?

Region is unsure, most likely Belgium, Wallonia (south)

 

Regards,

Simon

 

Edited May 14, 2020 by Stimon
Updated photo to show size (metric)

[Fossildude19]

Welcome to the Forum.

 

I assume you are talking about this item? 

 

 

To me, it looks like an adhering layer of micaceous matrix.

Sometimes, when rocks split, part of the matrix from one side will stick to the other in random shapes and sizes. 

 

As the perspective is tricky, if it is a depression in the matrix, then I would say it is the layer of matrix below the gray/black layer.

[Stimon]

Hey, thanks.

It looks like a depression to me so indeed it could be the other layer protruding. The shape, different roughness and also some edges laying free (as if there's play) made me think it could be another object. Thanks again for the speedy answer.