A PRELIMINARY REPORT ON CLAYS OE ELORIDA 
71 
out that this classification treats only the uses of clays for burned prod¬ 
ucts and such other uses, as paper and cloth filler, pigments, manufac¬ 
ture of Portland cement, etc., are not considered. He further states that: 
“This does not exclude clays from uses not specified. For example, r a 
superior fire clay may be suited for the manufacture of common brick. 
Its primary usefulness, however, may be regarded as for fire brick since 
it will be most valuable manufactured into that product^ 
Parmelee 1 states that a revised form of this classification is to ap¬ 
pear in an early issue of the Journal of the American Ceramic Society, 
and the classification as first published will, therefore, not be quoted here. 
iParmelee, C. W., private communication. 
CHAPTER HI 
MINERALOGY AND CHEMICAL PROPERTIES OF CLAYS 
MINERALS IN UNBURNED CLAYS 
Clay is composed essentially of a hydrous aluminum silicate, usually 
in the form of kaolinite with perhaps some of the minerals closely re¬ 
lated to it, varying amounts of colloidal matter, of either organic or min¬ 
eral character, and fragments of a great many different minerals rep¬ 
resenting chemically oxides, carbonates, silicates, hydroxides, etc. It 
will be seen then that clays may vary widely in their mineral and chemi¬ 
cal compositions. 
Kaolinite was formerly believed to be the basis of all clay, but this. 
view is now known to be erroneous. It is, however, very abundant in 
many clays. In one hundred and twelve samples of unburned clay ex¬ 
amined miroscopically by Somers 1 he reports kaolinite as scarce in only 
fourteen. It is a hydrous aluminum silicate represented by the formula 
AI 2 O 3 , 2Si02, and is composed then of 46.3 per cent silica (SiCL), 39.8 
per cent alumina (AI 2 O 3 ), and 13.9 per cent water (H 2 O). It is insolu¬ 
ble in hydrochloric acid and slowly soluble in hot sulphuric acid. It 
is always a secondary product and results from the alteration of other 
Corners, R. E., Microscopic Study of Clays, in U. S. Geol. Survey Bull. 708, 
p. 292, 1922. 
