From http://www.houzz.com/ideabooks/1362722.

Chinese slate floor tiles span the first floor. “We wanted to use the most irregular floor surface we could find. This room is used a lot, so we wanted to have a rough floor that we could walk on without worrying about damaging the floor,”

and the very small unit bamboo element wooden floor:

Bamboo has good eco credentials in terms of sustainable growth.
– but you need to check this.

I’d be biased towards bigger “elements”, so that it looks a bit more like wood until you look at the detail.

I’m less certain about the Chinese slate. Some comments suggest less than ideal extraction and transport etc. But I do like the idea of the rough textured surface and the size of the tiles in these examples.