Magma Tubes (A cave varient)

When mining deep underground in the overworld there should be a cave type called a magma tube. It'll be pretty circular and goes quite a distance. Some of the magma cubes could be dormant with obsidian, basalt and possibly blackstone whereas the actives could be filled with magma blocks, lava, and rare gems. I think this could be a great feature for people who want to explore underground