A PRELIMINARY REPORT ON CLAYS OF FLORIDA 71

out that this classification treats only the uses of clays for burned products and such other uses, as paper and cloth filler, pigments, manufacture of Portland cement, etc., are not considered. He further states that: "This does not exclude clays from uses not specified. For example, 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' states that a revised form of this classification is to appear in an early issue of the Journal of the American Ceramic Society, and the classification as first published will, therefore, not be quoted here.

 lParmelee, C. W., private communication.

 CHAPTER III

 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 related to it, varying amounts of colloidal matter, of either organic or mineral character, and fragments of a great many different minerals representing chemically oxides, carbonates, silicates, hydroxides, etc. It will be seen then that clays may vary widely in their mineral and chemical 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 examined miroscopically by Somers' he reports kaolinite as scarce in only fourteen. It is a hydrous aluminum silicate represented by the formula A1203, 2SiO2, and is composed then of 46.3 per cent silica (SiO2), 39.8 per cent alumina (A12O3), and 13.9 per cent water (H20). It is insoluble in hydrochloric acid and slowly soluble in hot sulphuric acid. It is always a secondary product and results from the alteration of other
 ISomers, R. E., Microscopic Study of Clays, in U. S. Geol. Survey Bull. 708, p. 292, 1922.