Petrified Wood (functional)

Petrified Wood. You're digging around caves, and see this log embedded into the ground, but it takes a pickaxe to mine? Boom, petrified wood. And it gets you a source for wood in the underground. Then to make it a useful thing, have it so that if you place wood underwater, it starts to rot, and eventually your build disintegrates. Use petrified wood instead, and it won't rot. Could even lead to some cool looking underwater wreck builds if they add a way to make those rotted logs become petrified before they're gone completely. You can still use it to make everything wooden (tools, sticks, chests, boats etc.), and either they're petrified from being crafted with the materials, or you add a system to petrify those things. Normal chests would degrade underwater over time, normal boats would slowly take damage if you keep them on top of the water, but the petrified ones won't. That will also give players a reason to actively seek out the block.