Mystery Stone.....any guesses?

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I bought this stone recently at a garage sale for $2. It was about 12" long by 2.5" wide. Originally it was used in a diesel repair shop and was mounted to a work station by some screws (screw holes drilled into each end of this stone). It was used to lap diesel injectors flat. Nowadays a diesel shop owner I know says it's typical to use a metal surface plate and fine lapping compounds.

It seems to be a mudstone of some variety. It's a hard stone, but the ends cut off fairly easily using a tile cutting round hack saw blade (2 slurry stones ya know). It's surface feels ultra smooth, definitely as smooth as coticule or Thuringian. The slurry stones do produce slurry easily. It does polish steel, but I've only had the time to do some passes with a razor needing a honing job.

It's colors are beautiful purples and grays with that very interesting black eye inclusion.

Howard Schechter viewing the same pictures thought it could be some sort of Wa****a Arkansas stone variety. He said the Wa****as came in a variety of colors. I thought Lily White Wa****as were classed at approx 1K grit. This stone is much much finer than that and is definitely only a polishing stone.

So.........any guesses?

Chris L

If it made a slurry and seems like a mudstone, then it shouldn't be an arkansas stone because the Novaculite doesn't act like that. Novaculite grit wants to remain in place, unlike a waterstone which releases grit readily and forms a slurry.

It could be a strange Belgian Blue...? Dick has a "Gray Begian" but that could just be a dull blue belgian, picture looks similar though. DICK GmbH Onlineshop Homepage

It could be ordinary old slate. I can't comment on the cutting properties but slate has been used as a whetstone in the past (as well as roof shingles, floor tiles etc. so maybe you can find a piece near by to compare:)).

Looks cool and sounds like a good stone regardless.

Congrats!

Maybe it is some form of slate? When I think slate, I think uniform gray or black, but I assume it can be multicolored?

Definitely produces slurry and has a smell similar to a coticule when being lapped, that clay kind of smell. I smeared some of the slurry on a sheet of white paper and let it dry to look at the "streak" as Howard Schechter calls it. It dried a perfectly uniform light gray.

Chris L

Yes, slate can be multicolored: Banded slate whetstones

The clay smell and uniform gray color suggest slate, or rather continue to rule out Arkansas. Do you have a Coticule with a slate back that could maybe serve as reference?

From the wikipedia description of slate: " Occasionally, as in the purple slates of North Wales, ferrous reduction spheres form around iron nuclei, leaving a light green spotted texture. These spheres are sometimes deformed by a subsequent applied stress field to ovoids, which appear as ellipses when viewed on a cleavage plane of the specimen."

..."Fine slate can also be used as a whetstone to hone knives."

So from those pics, it looks like you have a purple-ish/gray stone with green inclusions, almost exactly as is described above for Northern Wales Slate.

Yes, I have several slate bonded coticules. I think you're right, Russel. This stone is most likely a multi-colored slate. Cool.

Chris L

Great, now I have to get a piece for myself!

I've known about them for some time but ruled them out as good options, but if you say it polishes steel, it's worth a try. I wonder how long it would take to lap a floor tile, or maybe there are different grades.

You'll have to report back on this, very interesting.

I'll report back. I'm anxious to get enough time to really use it for edge polishing. It definitely polishes steel since it was used for years in a diesel shop to lap steel injectors flat.

The few passes I did on a razor just to see how quickly it altered a coarse stone scratch pattern looked like it might be a very.....slow.....polisher. But, I did not use slurry, etc. so experimentation is definitely necessary.

Chris L

I have what was advertised as a Wa****a stone that is oddly colored. It produces a purple slurry very similar to my BBW. It's a slow cutter/polisher and feels 'soft' on an edge.

Huh, I've never had an Arkansas stone that did that.

You learn something everyday.