Thread: New Natural African whetstones - followup

Hi Folks, (long post, picture heavy)

It's been a while since I've posted anything, having been completely occupied with finishing my design thesis (it went very well). But so I wanted to post about my latest adventures in hone-hunting here in my neck of the woods (SA). Some may recall my previous post on the 'Silkvein' hones that I came across, and actually at that time I had uncovered other new specimens that I've been really excited about, and so here I wanted to share it all with you guys, in the interest of discussing the properties of natural honing stones.


Firstly I'm no geologist, just a guy trying to make sense of terms and properties of stones that I learn from reading this and that, so please share any knowledge you may have on anything in this post.

Basically from my research into the geology of Kwa Zulu Natal (where I live) we have what's called the lower Ecca shale formation, which is some 250 million years old. This shale varies greatly, and is in many cases more of a cherty/shale structure, with iron oxide being present in the mix, giving a very red/orange natural 'skin' to the sides of some of the stones. There are shales that break through the surface of the ground and this shale is courser/easily crumbles, more sandstone-y, but then 15m and deeper beneath the surface, as well as some shale being in contact with intrusive dolerite dykes or sills, the shales are much harder/finer - this 'indurated' shale is where my interest lies, and is what I think I've identified in my new collected specimens.

The stones I've found sort of look like Japanese naturals, and from what I've read about the makeup of Jnats, they certainly are indurated, cherty shales(Please correct me if I'm wrong), some harder/softer than others, presenting a variety of different elements in their matrix, resulting in the beautiful varieties available.
In a way, I guess I'm asking, could there be a geological link between the stones I've found and Jnats? The world is a big place, and geologically there must be overlap here and there with regards to formation age, climate, and the properties of these natural meta-sedimentary stones.

Now, in some of the stones, you will see the orange 'skin' on the underside and sides of the stone, (just like on jnats) which is iron oxide(a natural abrasive interestingly enough). But you'll also notice most of the stones have a fine speckled dot pattern on the surface, and to me this looks strikingly similar to close-up images of the Tam o'shanter/scotch hones. (Which I believe are also indurated shales to some extent or another..) So it certainly feels like we're in the appropriate 'hone territory' here - wouldn't you agree? ... please, if you guys that own natural scotch hones could let me know if the dotted appearance in my images is similar to your hones, I don't own any scotch stones, so I've only seen images posted here on SRP.


I believe they are all in the 8k range, some higher for sure, based on tongue and tooth feel tests...(crazy fool I know) But I do think it's hard to tell without thoroughly testing them with a range of razors.. as sometimes a natural stone will feel not as physically smooth to the touch as another, yet it will yield a finer scratch and sharper edge when used.. So it's all yet to be properly established, as I've not had the time nor appropriate broad knowledge of hones to test them myself.


This is a long ramble of a post, my apologies indeed.
But what more can I say. I've been loosely grouping them into similar piles, but there are at least 3/4 distinct types that I've isolated. In the images you'll see two roughly cut large pieces(these two are very fine indeed), which I'm very excited to cut up, one will be a MASSIVE hone for my private collection.
The wedge shaped piece was taken from the smaller of these large chunks, this is the stone that is greeny/grey with red streaks throughout.

Here are images I took today of the selection as described above. PLENTY OF PICS, because we all love pictures.

Thanks guys for letting me babble, hope it strikes up some discussion on hone stones, and perhaps some insights into what my specimens may be - geologically.

Sincerely
- Mike

Hi Jasper,

Thanks for the info and pictures!
Do you find that using slurry with the hone with the elongated speckles (picture 15) causes chipping but with water gives a very smooth sharp edge?

regards,

Torolf

Hi Torolf,
I've not encountered any chipping (assume you mean on the blades edge) with any of the hones pictured. The slurry speeds up the cutting, and finishing with just clear water will yield the finest edge the stone can offer. This is the case with most slurry forming stones.

Yes, just wondering what you find. I have a stone which is remarkably similar and when used like a barber hone has incredible effect. When used with slurry appears to cause micro chipping. Whether the slurry increases the speed to the point of edge degradation or there is a release of damaging particles, I don't know. But it also seems to happen with a higher lap count on water (again, slurry release or just very fast cutter...).

I find it funny due to the utter smoothness of the edge when this stone is used sparingly. But I haven't had time to pin it down yet (or identify where the stone comes from...)

regards,
Torolf

My first post here in this forum.
I am living is Japan and I am a researcher in Chemistry.
So I do not have a background in geology.

But I think I can help a bit from the academic side.
I found a scientific report on "toishi type" siliceous shale here:

http://www.gsj.jp/Pub/Bull/vol_44/44-12_01.pdf

The author is Makoto Musashino and his joint author database is here:

nkysdb: æ¦èâ€�µé‡Ž 実

I think you can ask some of these Professors for help.

If the mine you found these stones are like the toishi mines in Kyoto it should have many strata (or layers).

Search for thin strata (layer) if you are looking for more dense and fine stones.

In general the strata which produce the finest stone in Kyoto are thin too. It is because sediment speed per year is little for smaller sediments and so the fine stone layer is thin.

Hope it helps.

I've been digging around a bit more, looking into the term 'indurated shale' and I've uncovered that the word 'Lydianite' seems to be synonymous. Now, from previous knowledge, I believe Lydianite is a classical term for Lydia Stones, which were/are used by jewellers to test for gold. They are also called 'Touch stones' I believe. Nonetheless, these Lydia stones are very fine uniform stones.

In addition, 'Indurated Shale' also seems to be synonymous with 'Hornfels' which is a rock type, and this term specifically seems to come up in papers relating to my exact part of the world. Hornfels is also referred to as 'Whetstone' in a few UK papers I've seen, so it's looking pretty good that my stones are indeed indurated shales/Lydianite/hornfels. And I do believe the Scotch hones - WOA, Tam o'shanter etc, and indeed referred to as Hornfels, so this is all pretty interesting..

Anyone have any more thoughts on this?

This is taken from the 'Catalogue of Stone Age Artefacts from Southern Africa in The British Museum' :

"Hornfels: A generally quite fine-grained, greyish-black
metamorphic rock produced by the metamorphosis of shale
or mudstone and available either from specific point
sources along dolerite dykes or eroded out in stream beds.
Hornfels acquires a patina that varies from light grey to
orange-red with age. Indurated shale and lydianite are
synonyms that may be found in the older literature."

Seems interesting no? Especially the note on the orange/red patina..

Jasper, I'm following this with great interest.

I of course think it more than likely that there are deposits of stones with honing qualities like those of the Japanese stones all over e world. The only real reson for the fame/number of the good Japanese hones is the market--Japan has had a huge hunger for good, consistent honing stones for a good thousand year, and so the search was worth it.

I'm trying to understand the petrology/geology of the Japanese stones myself, but the materialI have is all in Japanese and my translation attempts are slow at best.

ところで、中先生へよこそSRPへ！載せたPDFは有難う御座いました。今からも宜しくお願い します。

This is really interesting and I'm fascinated. Is there any chance of getting a small sample to test out here in Canada? I'm curious to know how quickly the slurry cuts and how well it polishes with water.

Thanks Jim, your interest is much appreciated indeed.
It would be great if you managed to share with me anything you learn regarding the geology of Japanese naturals..
This new info I've posted above regarding Hornfels seems very likely to be where my stones fit in the spectrum, but, I'm still questioning a few things: Firstly, if Scotch hones are indeed 'Hornfels' (indurated shale) then why have I never seen any images of Scotch hones with any orange-red parts, either in the matrix or on the sides etc of the hones? This leads me to believe, as the excerpt above explains, that the orange-red patina develops WITH AGE, so perhaps the scotch hones are younger than my African stones? Perhaps the article is specifically referring to Hornfels from Southern Africa, and this orange skin/patina is location specific?

But then again, there is no denying the visual link between my stones and Japanese naturals, so what is the connection between 'Hornfels' and the Jnats, are Jnats perhaps a form of Hornfels as well? I know some Japanese stones do have a similar speckled/dotted appearance like my stones and indeed the Scotch hones, so geologically there seems to be a link between all of them...