While doing research on natural sharpening stones I stumbled across several woodworking forums that mentioned petrified wood can be used as an alternate sharpening stone and that specifically petrified palm wood was the best. Petrified palm wood is actually called Palmoxyln and is an extinct genus of palm. This sample is from Louisiana and considered very scarce. It's also porous so the swarf flows off the stone freely and the texture is just right for sharpening.
I found this sample of petrified palm wood on eBay for $14 so I figured I'd give it a try. The slab is a nice size for sharpening plane blades. I cut a scrap piece of rosewood as a base plate to prevent the stone from breaking under pressure. A little bit of 5-minute epoxy, and our stone is ready for action.
I used a natural nagura stone to work up a thick creamy slurry.
The petrified palm tree was very slow to cut, but it did put a nice mirror finish on the back of the blade. This was after about 1000 strokes. This stone contains a lot of white agate which is mycrocrystaline quartz which shows that not all stones of the same type are equal. I believe if this stone contained more petrified wood than agate, it may have cut metal faster. In comparison, the brown edges of this stone did the most work while the white center core (agate) removed the least amount of metal. As you can see, the dark swarf buildup in the pours shows promise. This stone has potential but would not be my 'go to' stone. My red jasper still sits on top of that list.
Another stone that was mentioned in the woodworking forums as a natural sharpening stone is Malachite. Malachite is a bright green mineral consisting of copper hydroxyl carbonate. Many years ago I acquired a sample of Malachite and it's been sitting in my backyard ever since. Last summer I placed it on the hearth of my outdoor fireplace. After reading the woodworker forum I thought I would give it a try.
This is a beautiful stone and 3 sides have already been cut flat with a diamond saw. There appears to be a good amount of quartz in this particular sample.
After 100 strokes I started to lose the mirror finish from the petrified palm wood and I didn't see much swarf developing. Using the nagura didn't help much either. I am curious how this stone would work as an intermediate stone. I believe the high content of quartz in this sample diminished the sharpening potential of this stone.
I would like to cut another side of this stone that shows more Malachite than quartz and see how that compares.
The petrified palm, malachite, ODC nagura and Japanese nagura resting on my sharpening pond.
More experiments to follow. I'll leave you with some photos of my stones. Thanks for reading.