Wow it's a cool piece, almost looks like a fossil, I wouldn't know of what though, the host rock looks like a shale to me, I hope someone chimes in with a definite answer, its a keeper in my opinion, very cool
Whats that round circle in the first photo? Have you tried tapping on it lightly to see if it's hollow because that vein looks like it goes behind that round structure and it might be a geode. The veins possibly Opal and the rock possibly basalt.... I'm throwing that out of my butt.
Sedimentary rock (possibly limestone?) with a concretion (the round ball) and quartz veins.
The quartz veins are more resistant to erosion, thus they protrude from the limestone mass which eroded away quicker.