646 GEOLOGY OF OHIO. 
There can be but little generalizing as to the tendencies of the 
different qualities of clay to be out of the kaolin ratio or in it. The 
comparison of a large number of results obtained from such analysis has 
yet to be undertaken. 
The mineralogical structure, then, appears to be worthy of con- 
sideration, as well as the chemical one, in examinations of clays with 
reference to their value. 
The minerals going to compose clay are kaolinite, quartz, mica, 
feldspar, oxide of iron, lime and magnesia, probably as silicates, the 
alkalies, probably present in the mica and feldspar, sulphide of iron, 
titanate of iron, and various rare constituents such as cobalt, copper, 
zinc, etc. 
It must not be supposed that all of these minerals are found in each 
clay, but such minerals are found in examining any considerable num- 
ber of clays. Kaolinite, as already mentioned, is a hydrous silicate of 
alumina, having a percentage composition of 
SHCA (SUGOD eecieucchcodsecescsseorscacecceranedccocscceconncaete tetas a antennae 46.3 
A Tamminvay CALVO): .ccscisectecensccccscacecdchescdsoes cena aceneeoat eeotetnene antes 39.8 
Water, (EUS O) 25s senile s troveaieslsteseas soeinceteintociet cect testae sacactecmacemeceueeer cuseee 13.9 
100.0 
which is represented by the chemical formula 
Al, O;, 2 Si O, + 2 HO 
When pure, it occurs rarely in small pearly scales or plates of a 
definite crystalline shape, but commonly it is found in large masses of a 
mealy nature. It is white or nearly so, sometimes with a pearly lustre, 
and sometimes with none, and an unctuous, soapy feel. ‘The properties 
which make ordinary clay so valuable are of course characteristic of this 
body in a greater degree. 
Quartz is one of the impurities in clay which is always present ; no 
clay is free from it, though the finest kaolins in New Jersey show only 
two-tenths of one per cent. In the other extreme there is no well-marked 
line between sandstone and clay; since almost any sandrock shows 
alumina and water which immediately indicates the presence of clay, so 
that it is hard to say where the sandy clay ends and the clayey sandrock 
begins. Quartz is in grains varying from z5-in. to dust in the finest 
state of division ; occasionally pebbles of large size are found in clay, but 
the body of the quartz present, falls between the limits assigned. It is 
beautiful white sand, with its edges perfect and sharp, and that which is 
