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Specific Gravity Confusion

I think the basic problem is that density is a correlation to grit, but it's just that.
In noviculite, it's canon. density shows grit.
Black and transparent have the same density, yet in testing, they show different grits.
 

Legion

Staff member
I think the basic problem is that density is a correlation to grit, but it's just that.
In noviculite, it's canon. density shows grit.
Black and transparent have the same density, yet in testing, they show different grits.
My understanding of Arkansas is that it is all the same "grit". But as the density increases the particles of silica become more tightly packed, giving a finer edge. Also, the dense ones are less friable, again making them finer.

Different to a synthetic stone, which has cutting particles of different sizes, or grit, suspended in a matrix.
 
Arks have a PSD spread too. The range is pretty wide.
From grade to grade they all have a similar PSD though.
That's Arks - not every Novaculite.
Yes, how packed the Ark is becomes part of the story. Washita are less dense and coarser than hard Arks.
A translucent Ark with a SG of 2.7 is not necessarily finer than a SB Ark with a SG of 2.5 though....

With a synth the maker buys a pound or a ton of lab made Alox where every particle has the same basic crystalline structure, and it is all sifted to to be within a certain particle size range, and then put into a binder to meet a spec of how much abrasive per cubic centimeter.

With Arks, some of that concept applies, but there is a diverse crystalline texture that plays heavily into the mix. Particle size spread in Arks is pretty wide.
It's too much to get into here, really. A brief glimpse into could be comparing an Ark to Chalcedony, also very high in SIO2, silica, SG is roughly 2.6 - but not a great hone. Why? Because the SIO2 in Chalcedony is not formed the same way as what we see in an Arkansas stone... both are SIO2 but their 'bones' come from different systems.
 
The coloring scheme, hematite red, iron black, etc - is a characteristic seen in Cherts - Novaculite is a form of chert. It's referenced in many places but one source I remember offhand is a paper on the Texas Novaculite deposits. Other places included papers or articles written by orgs in Hot Springs, a paper written by Ashley, forget the title but it had to do with outcroppings, and at least one piece by Arkansas Geological. I don't keep footnotes, they're too difficult to organize. Lab analysis done in Russia, checking psd, impurities, etc, also listed Iron for the black sample, it was not present in the translucent sample. I canont recall if carbon showed up in that analysis. In the grand scheme of things I don't suppose any of it matters, my reason for mentioning thiron and hematite was their fairly high SG. Manganese is another impurity associated with novaculite but I can't remember the details, also high SG.

Books from the 'old days' are great but sometimes the info is dated, has been superseded or just dismissed. I've read the Geological Surveys, Griswold's book too. Those writings were enlightening, just like Leske's cabinet was enlightening.

If we go back far enough we find Novaculite classed as Argillaceaus, and not Silaceous.
In the 1890s stones we refer to as Jnats were classed as Slate, today we class as shale.
I would very much like to see what has been done lately and get some up to date information. In the 1890 survey they figured it was carbon based on loss through ignition and that was at only % 0.09. Enough to turn an ark black as coal? Safe to assume the translucent didn't show loss through ignition?


I have seen quotes mentioning Arks being better than %99 pure. Have you come across any information on the purity and if there could be enough impurity to measure or effect the SPG?

Thanks for sharing.
 
Searching via google, academic writing platforms, etc - information becomes available. Some old, some not so old, some fairly recent. Current analysis of Arkansas Novaculite does not show carbon in the list of impurities for samples tested at that time.
I do not recall any source saying every single piece of Novaculite from anywhere is 99% silica.
But I have seen entries where that purity level was found to be true for tested examples, etc.
Playing with the math suggests that impurities @ 1% could impact SG. Any material in the stone that does not have the same SG as the rest of the stone could do that.
The bigger issue is going to be the stones porosity/density in general. White washita were less dense than white soft Arks. Not because of shades of grey color, but how the stone formed via diagenesis.
The difference from Washita to Hard Ark is 2.25 to 2.5 SG - not a big span.
 
Searching via google, academic writing platforms, etc - information becomes available. Some old, some not so old, some fairly recent. Current analysis of Arkansas Novaculite does not show carbon in the list of impurities for samples tested at that time.
I do not recall any source saying every single piece of Novaculite from anywhere is 99% silica.
But I have seen entries where that purity level was found to be true for tested examples, etc.
Playing with the math suggests that impurities @ 1% could impact SG. Any material in the stone that does not have the same SG as the rest of the stone could do that.
The bigger issue is going to be the stones porosity/density in general. White washita were less dense than white soft Arks. Not because of shades of grey color, but how the stone formed via diagenesis.
The difference from Washita to Hard Ark is 2.25 to 2.5 SG - not a big span.
The carbon in arkansas stones is on my previously cited source on page 135. Quote...

"coloring matter is very small ; it is probably carbon, as in the black Ouachita stone."

So yes, unless they are mistaken there is carbon in the black Washita and they think the black Ark as well.

Page 90 gives an average of %99.5 silica in arkansas stones.

Why is carbon not listed but talked about? I don't know, the test method used couldn't identify it maybe, perhaps it went out the chimney on ignition? Coming up with %100.30 is problematic also. But lacking any other data about Arkansas stones specifically this is the best I know of.

ttps://www.google.com/books/edition/Annual_Report_of_the_Geological_Survey_o/y7q_AAAAIAAJ?hl=en&gbpv=1&dq=washita+stones+arkansas+geological+survey&pg=PA91&printsec=frontcover#v=onepage&q&f=false
 
Information changes when new technologies shed new light on old subjects.
When those surveys were written, many scientists and doctors were still subscribing to the Miasma theory.
Things have changed a lot in the last 125+ years.
FWIW - "Science" is wrong quite often, that's part of the process actually.

Modern chemical and spectral analysis, along with processes like NAA weren't available in the 1890s.
So it's possible that modern scientific processes could yield very different data that what was possible long ago.
If modern scientific analysis didn't identify carbon in a sample of Arkansas Novaculite, I am going to believe that there was no carbon in the sample they tested. What is in every single piece of Arkansas Novaculite though, will be forever unknown because not ever piece of stone gets tested. As for the current list of impurities, i have no reason to believe it's incomplete or incorrect. It's just test data. Whether the impurity is iron or manganese, whether it's 1/2% or 2%, or whatever, it is what it is.

Maybe some variants of Arkansas Novaculite have carbon, maybe not, I haven't done any testing myself but I do know that samples taken from different locations have yielded different test results so far as density and textures go. But I haven't come across any recent test data listing carbon as being in the mix. If an Ark has .5% -1% or 2% carbon or iron or manganese, or whatever, it's really not important.
The concern here seems like mental masturbation for no reason.

I've just realized that this sidebar convo has derailed the thread significantly; and I am way past my personal limit for posts in a single thread anyway. I should know better, and to be fair to the OP and this thread, this distraction belongs in another thread.
Or maybe in another forum.
 
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