I'm having some difficulties reproducing the veins effect in the stone. I can't find a way to make them run along a direction and randomly split here and there.
I am using a Voronoi texture but the lines tend to wrap around themselves (creating rings and semi-circles) or they overlap too much. For the test render, I had to fine-tune the scale of the textures in order to achieve a somewhat acceptable result, and it's still very far from the desired effect.
Desired effect (at the end of the linked page, under "Variations", you can find different examples): https://www.leaceramiche.com/collection/nextone
My attempt (too few veins and they are not splitting like in the desired effect, if I try to increase their number they wrap around and overlap with each other. Ignore the difference in colour, for the moment):
Nodes (a lot of trial and error here):
