In the matter of woods that are hard and woods that are soft, it's important to remember that soft woods can harden up and vice versa. Let's take a moment to discuss my usual opponent, petrified pine.
Now, we all know that green pine is pretty soft, right? Right. Hell, if the trunk is less than 4" or so diameter, I don't even need an edged tool to bring it down...the weight of my body, some enthusiastic wrestling, and plenty of cursing will get the job done. When tools are used they keep an edge pretty much indefinitely on the stuff.
Now, let's take a pine that's been growing for a few decades and has led a rough life. The soil is poor. It floods in the spring and fall, there's drought in the summer, snow and ice in the winter and strong winds year round. Bucks and other critters tear up the bark all the time. Bugs bore holes in the trunk. After fifty years or so of this the poor tree gives it up and dies - and remains standing for a few decades more.
This is not soft wood anymore.
The heartwood is impregnated with sap that, over the years, hardened up just like epoxy. If you were to remove a chunk of that wood you'd find that it looks and feels like very hard plastic. Axes and khukuris bounce off the stuff, and if all you've got is a 'hawk or hatchet, don't even waste your time - just find another source of wood. If you do have the time and the calories to spare, and you chop through it, you'll find that your blade is too hot to touch afterwards.
All that...from pine. A soft wood. There are some other woods that change their nature depending on when and how they're harvested, how they're cured, etc., and our resident woodchucks can tell us more about it.
My madrona staves cracked, unfortunately, and I was planning on using them for handles, but now that I think about it, petrified pine wouldn't be bad either. (Naturally stabilized wood? I can't imagine this stuff absorbing water...)