Blue/green/gray stone

[PaulFLUS]

Wonder if anyone recognizes this rock. I was pretty sure it was a synth but now I'm not sure. I got it a while ago with a bunch of Arks, a knife sharpening lot all filthy and oily.



I soaked it for a few days in some simple green and it came back this blue green color with a grayish hue. I put the bill there for color reference. I have not lapped or flattened it since it was pretty well flat when I got it.

They were using oil on it. It will let a drop of water sit on it and not suck it up but since it had oil on it I'm not sure it would soak it up before oil soaked.

It has about the same consistency as an India Stone but it hones finer, finer than 6k, maybe coarser than 8k, I'd estimate 7-8-ish. It cuts fast and smooth. I like the feel and the edge it leaves. It seems like a good medium range stone but, as I say, I have not lapped it so i'm not sure what it's boundaries are.

Dimensions are 6"X2"X1/2". Edges and corners were chamfered already when I got it.

[stoneandstrop]

Generic slate from the look of it.
Maybe it gave a finer edge with oil and why the last person used it that way, no idea really.

[thebigspendur]

Yea looks like slate but with time and use any natural rock weathers and stains and the outside often times is quite different than the inside. If you know someone with a small sandblaster you would know rite quick.

[PaulFLUS]

It seems a little hard for slate. I was sure at first it was synthetic. I tried the puddle of vinegar trick. No fizzy bubbles, but I'm not sure how effective that is eanyway specially since it was soaked full of oil.

EDIT: One thing I did do just yesterday was run in across some 320 W/D. It produced a greenish gray slurry, but not a lot of it. But then really it was just a test and not a lapping.

[stoneandstrop]

Slates can be pretty hard at times IMO.
Thuries are on the soft side for sure but my purple Welsh slate is the complete opposite. I've had razors that did not like an Escher hone but honed beautifully on the Welsh one.
The Vermont slates are also much, much harder as well.

[PaulFLUS]

I was thinking chrome oxide synth until I did the W/D test. Boy that slurry sure looked like slate slurry, thin and milky.

[thebigspendur]

Slate is Fe2O3+SiO2+Al2O3+CaO+MgO. Depending on the amount of calcium the acid test may or may not work and the acid may have to stay on the rock for a time.


The old rockhounds' test for slate is if you hit it with a hammer it makes kind of a ringing or high pitched sound. Don't hit it too hard cause slate can cleave into sheets kind of like Mica.

[PaulFLUS]

I'll try that tap/ring test in the morning.

[stoneandstrop]

Slates do not generally make a high pitched ring when tapped IMO.
Quite the opposite. More of a low pitch, almost a thud with an Escher.
Novaculite, hard Jnat etc give a very high pitched ring.
A subjective test for density.
If you have another known slate you can compare to that, you will have a much better idea.
Compare to other stones you know to judge hardness against them.
Of course a specific gravity test will get you much closer

[thebigspendur]

Yea, take two pieces of slate and tap them together and you get the distinctive sound. The thinner the material the more the characteristic sound. Ever hear slate roofing tiles tap each other?

This is a tried and true pro test going back a couple hundred years.