As a further analysis of the probable mineral make-up of clays, Grout's data will be discussed by groups. In this only the most com mon and abundant minerals known to occur in clays are considered.
Coarsest grade (0.15 mm.) : This grade of grain, even if all the alkali is considered as being present as a constituent part of feldspar grains, would be assumed to be composed almost entirely of non-dis integrated kaolin and quartz grains. Only in one case, however, does Mr. Grout' speak of the physical character of the grains of this grade. In this particular case the clay examined is a shale. "The 12.9 per cent (referring to coarse sand grade) on 3 mm. screen was mostly flat scales of shale, about 5 mm. in size, of red and greenish color." The total absence of similar description of this grade in the other 25 samples justifies the conclusion that the grains of this grade were flat or scale like only in this one sample. If this conclusion is true, then it is fair to assume that either. the kaolin scales are present in undissolvable bundles, or these grains are not composed of kaolin but some other aluminum compound like gibbsite, etc.
On the other hand, it is hardly possible that grains of feldspar of this size could remain unaltered in these old river clays that have been elutriated, mixed and moved by fresh waters possibly for ages. There is justification for the assumption, therefore, that these coarse grains are bundles of kaolinitic grains cemented together so tightly by some salt that they resist disintegration by water. If the alkalies had been present as constituent parts of feldspar grains of this size, the feldspar crystals could have been easily recognized under the microscope as cubical grains and not flat scales.
H. B. Fox, in the Ceramic laboratories of the University of Illinois, separated the grains of a shale and a glacial clay into the several grades of fineness, and found that all the grades possessed a plasticity that varied directly with the fineness of grain, and that the coarse grains which could not be disintegrated by 20 hours of constant shaking in water, when broken down in a mortar, developed plasticity that in creased as the size of the grains decreased, until when the coarse grains had been reduced to an impalpable powder they developed a plasticity nearly equal to that exhibited in the finest grains that had been separ ated from the original sample, showing, it is believed, that the coarser grains were comprised of materials similar in every respect to those in the fine grains, but cemented in such a way that they withstood success fully the disintegration treatment.
(0.02 to 0.15) grade: It is highly improbable that this grade con tained no kaolin or clay substance, but such would have to be the case if all the alkali was present as a constituent part of the orthoclase feld spar grains. The alkalies cannot be present in this case as easily soluble salts, for the alkaline salts would have been dissolved, carried in solu tion, and would affect only the finest grades. If the feldspar was oligo clase and not orthoclase, then the 0.5 equiyalents of the alumina could be considered as a constituent of kaolin grains.
Although there is no statement made as to the presence of mica in the clays from which these grades of grains were obtained, Mr. Grim sley' states that it is a very common constitutent of the West Virginia clays. Stull' gives as the chemical formula of common muscovite mica the following : 0.1213 Ca0 0.1103 MgO.... j 1.000 A1,0, ............ 16.399 SiO —0 974 H,Q 0.3290 K,0 ............ 0.18S7 Fe,O, .................. Comb. Wt.582.187 0.0929 Na,O.
On the assumption that the alkali in this grade is derived wholly from muscovite mica of the composition given by Stull, the mineral constitu tents of this grade of grain might be proportioned as shown by the following calculations: In this case, the formula most favorable to the supposition that all the K=0 is present in the form of mica has been taken. If the theoret ical formula K=0, 3 A1=0=, 6 Si 02, 2 H=0 had been taken, there would have been either considerable K=0 to account for in some other way, or return to the original hypothesis that this group contained no kaolin. Either supposition leaves considerable alkali unaccounted for, which as has been pointed out, could not possibly be present in an early soluble form.