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.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.
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?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Books from the 'old days' are great but sometimes the info is dated, has been superseded or just dismissed.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.
The carbon in arkansas stones is on my previously cited source on page 135. Quote...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.