plant fossil, modern roots, natural fired terracota or other?

[tlatoanitzin]

here is a bed of this rock in a mountain, I took off a chunk of it with my hand and carried home, when staying in home I took the rock and separated with my hands in halves very easily, then I observed that it had this kind of biological features or what it seemed to me, in both halves. The first I thought it was some kind of root that was got into the rock, but then I remembered that the chunk was shut. I noted that it had two layers of this material, one different to the other, I ended up destroying one layer, in order to photograph the one with more remarkable features. I would like to know if the biological features are present because the chunk of rock is a fossil or if it is just a mineral.
unknown_rock_I - a set on Flickr