I had heard somewhere that you could use petrified wood as a sharpening stone. Hmmmm......
The small piece was a test and.... it actually did something! Go figure. It is no surprise that it would scratch the metal since petrified wood isn't actually wood at all, but more of a wood shaped piece of quartz. The process is called permineralization and the Wikipedia gods will tell you all you need to know about that. I, on the other hand, can tell you how to sharpen a chisel using a fossil. Maybe I can contribute an entry?
Anyway, what surprised me was that the scratch pattern was actually fairly even with a slow, but respectable, rate of metal removal. It even felt like a sharpening stone. Decent feedback, a tendency to"squeak" and grab-the-earth at times, and VERY little slurry production because the stuff is pretty hard. That said, it only took me about 15 minutes to turn this chunk of fossil into a sharpening stone.
I polished the flat grain face to 1200 grit and when I get around to it, I'll stick it onto a piece of stone to anchor it.
While not the fastest stone around, it is definitely a keeper. My wife's grandfather picked it up who knows how long ago, so it has history in more ways than one. And it looks cool!
How did it work?
We'll start with the Frankenstone (3000-5000)
Too hard, needs slurry.
DMT 1200 diamond nagura.
Black swarf ( it's working!)
Not too bad...kinda slow, but pretty smooth, some scratches but shallow.
Not a full mirror, but close. Definitely shiny steel and some superficial shine to the iron/jigane.
Control/reality-check. Ozuku asagi. Faster, smoother, and only the finest of scratches. Perhaps not a fair comparison?
The green mystery inkstone. This feels very similar in use and the scratch pattern is similar. This IS faster, though.
Faster metal removal, smoother action and just all-around easier to use. The ODC gives a nice even matte finish to the jigane. I like that.
Still WAY better. Ozuku asagi w/ODC. Faster, smoother, easier. Nice definition.
Well, you can't have too many sharpening stones. This was just sitting in a shoebox and, surprise surprise, it works like your average super-hard Japanese natural waterstone. Not the greatest, but definitely interesting. I looked at some other pieces of petrified wood at a store in town, most of which looked like rocks. Agate or something. This piece is probably an example of incomplete metamorphosis and still looks a fair bit like wood. A conifer of some sort.
When I first got interested in natural sharpening stones, I thought that they were very rare and special (well, the best ones ARE!) but it turns out that the darn things are everywhere. The trick is to first learn how to use natural stones and having a "real" sharpening stone will help. That way, if you are having problems, you will know that the fault lies with your technique. The stone is a known quantity. The second thing would be that a nice stone makes sharpening fun ( well, some of us are easily entertained....), but a bad one will keep you from ever learning anything because you won't use the darn thing. Then you're back to the whole dull tool situation. Also, as you get better, your preferences and priorities will change, so don't sell the farm just to buy into some system. Ebay is full of "systems" that someone else outgrew. At the least, buy used and let someone else pay the depreciation.
I wish that I had learned some of this stuff sooner.