If you type pseudofossil into the image search engine section of Google, images like the ones shown below will start to appear. These mineral deposits of manganese oxide were created when mineral enriched water seeped into the cracks of this rock. After the water departed, these mineral patterns were left.
The patterns remind me of a little branching plant or fractals defined by mathematics.
This rock is probably Devonian so these pattern formed sometime in the last 400 million years.