Looking at it closely with a loupe and microscope you can see the layered look like a slate, but the layers look like they are made up of flakes like how graphite or coal looks
yes mine looks the same way , graphite like layers, with very fine shiney flakes .It is a some kind of a mudstone , works realy well .
the only problem ,is that is soft and it digs it self quickly , but the stone works fantastic .
I dont have a microscope 1000 magnification , only my beard , sory .