stone ID

[northpaw]

I picked up a few rocks while walking in the nearby mountains with the intention of lapping them to see what I could see. Two turned out to be duds, but this one is much more interesting.

For starters, it's very, very hard. It's been harder to lap than anything else I have (C12k, barber's hone, etc.). As you might be able to see in the pic, there are no visible grains in the greenish areas - only tiny layer-like lines. The lack of grains is what originally caught my eye.

After getting it flat and smoothing out any edges that could catch a razor, I took an already-sharp razor and did a bunch of passes with a lot of water on the stone. Didn't seem to dull the edge. If anything, it felt sharper on my thumb pad. I noticed that the stone absorbs water fairly quickly, so I started just lightly misting the surface and honing until it was dry (probably 20 passes each time). Felt like it started to build a tiny bit of slurry as it dried.

Shaved with the test blade today and got the best shave I've ever had from that particular razor. One benchmark was that I was able to shave my upper lip against the grain with the spine completely flat on my face. The only other time I've been able to do that consistently is off of my Shapton 30k.

Anyway, I know it could be some kind of fluke, but I'm curious if anyone knows what kind of rock this is. Should I head back up the mountain with a pickup truck?

(click for larger pic)

[Piet]

Great find, but what are you still doing here? Go back and look for more

What is the size of the stone?

[northpaw]

It's a big chunk of rock. With the right (diamond?) saw, one could probably get 4 or 5 hones out of it.

I really wanted to flatten one of its large faces, but after an hour or so with little progress, I settled for a smaller side that was almost perfectly flat to begin with. This lapped side is roughly 13cm x 6cm (5"x2.5")

Sure wish I could get the big face lapped. It ain't happening with sandpaper, though.

[Kingfish]

Adam,
Do you mean the side we are looking at came that way? It allready looks like it was cut intentionally and partially lapped.
Mike

[northpaw]

Adam,
Do you mean the side we are looking at came that way? It allready looks like it was cut intentionally and partially lapped.
Mike

This side I ended up using was very flat, but no, I don't think it had been cut before I found it and lapped it. It only looks that way now after several hours on about 3 meters of (now ruined) 80 grit sandpaper strip .

[A_S]

There was a razor hone of considerable repute that was found in the Arbuckle Mountains that was composed of indurated sandstone. The stone was indurated to a depth of 125 ft, but it was the stone on the surface that was the most prized, as weathering had erased the grain of the stone rendering it completely smooth. When you mentioned the lack of grain in your stone, this was the first thing that came to mind. Also, the porousity that you mention is typical of sandstones as well.
Alternatively, based soley on the colouring, it may be a modification of chloritic slate, various hones of this nature can be found all over the world.

Kindest regards,
Alex

[Kingfish]

Adam,
If one of the "Rock Jocks" is going to help with an ID, it might be helpful to take a couple of close ups where the specimen naturally broke. The cleavage or lack there of means lots to the Geologically inclined.
Working with nature in the raw makes you think back to a time when our ancestors where rubbing a piece of bronze or iron on such a specimen. Maybe it was someone elses finishing stone long ago Adam? Maybe there was a tribal leader named Lynn of "The Clan of The Straight Razor Place" , and warriors would gather round the fire and show off their new stones and what they can do.
Mike

[JimmyHAD]

Great looking rock Adam. At first glance I thought it was one of the J-nats.

Alex, just curious, I googled indurated to find that it meant hardened. What might have indurated the sandstone to the depth of 125 feet ? The first thing that comes to my mind is glaciers shifting and work hardening the rock. Anything to that ? Is the cause known ?

[Piet]

This side I ended up using was very flat, but no, I don't think it had been cut before I found it and lapped it. It only looks that way now after several hours on about 3 meters of (now ruined) 80 grit sandpaper strip .

80 grit sandpaper doesn't work that well for lapping, I know because I wasted a lot of hours trying to lap a swaty with it. A coarse DMT or even a cheap diamant stone will work much better. Wet 120 waterproof sandpaper will also work better.

[A_S]

The main cause for induration is compression in one form of another, glacial movement, contact with harder strata or simply because lower strata have more weight on them than the upper layers. Heat can also turn certain rocks into whetstones or hones. Weathering too, can play a part in this process, but in many cases weathering will destroy stone rather than hardening it, like the novacuite of Carp River.

There are examples of hones produced by the various methods of compression to be found in the literature. Slate from Hestercombe in England and Novaculite from Bald's Head, Maine are hardened by contact with Syenitic Dykes and Quartz dykes respectively. At Hestercombe, the induration turns the ordinary slate into honestones, but at Bald's Head, it is the material farthest away from the dykes which is most desirable, as the novaculite in contact with the quartz has too splintery a fracture to be of much use.

In Wales, there are many areas where the slate has been metamorphosed into honestones due to contact with greenstone. The greenstone initially compresses, and ultimately intrudes into, the slate forming a spotted rock known as Snakestone. This is very common in Caernarvonshire and several localities were exploited as a source of honestones.

Examples of hones that are produced by virtue of being found at an increased depth include Hindostan stones, where the lower layers are preferred due to being harder and less friable; and also hones that were found at a very great depth when digging a well in Hampstead, England.

Baked shales and baked mudstones producing hones are found in Ayr, the TOS, and at Enterkine Quarry in Tarbolton, respectively. There is also a baked and compressed shale that was used for whetstones in Teesdale, England.

Another factor that can cause hardening and metamorphosis of other rocks into hones is the presence of iron ore. There were certain grades of Hindostan that contained considerable quantities of iron and these were preferred because they were less friable than the regular sandstone used to make the Hindostan whetstones. There is another honestone from Indiana, known as the Fera Hone-stone, that was very highly regarded. This was a clay-slate that contained iron. Unfortunately, this type of hone was only produced commercially by one quarry, and therefore supply was very limited.

Also, many different types of hones were processed after extraction by either boiling in oil or baking at very high temperatures. Examples of the former include: Turkey Hones, Chapel Hill Novaculite from North Carolina and the Devil's Punch Bowl Whetstone from the Mangerton Mountains in Ireland. Stones that were baked to improve their performance include the Norway Ragstones, the Kentucky Caron Hone and a hone from Virginia about which I have been unable to find out anything more.

Incidentally, the sandstone from the Arbuckle Mountains, was so hard that it causes saprks to fly when struck with steel.

Hope this is of at least some help or interest to you.

Kindest regards,
Alex