A PRELIMINARY REPORT ON CLAYS OE ELORIDA 
77 
Hornblende —This is a complex silicate frequently found in some 
impure clays. It weathers readily and colors the clay red, owing prob¬ 
ably to its iron content. 
Garnet —This is another complex silicate, which occurs as grains 
in some impure clays. Its effect is similar to that of hornblende. 
Vkianite —Fe 3 P 20 s, 8 H 2 O. A hydrous ferrous phosphate which 
may occur in some clays. It is not a common constituent of clays, but 
occurs in some Atlantic coast clays as small blue spots. Its presence in 
large quantities has not been determined. 
Pyrolusite —MnC >2 j 
Psilomelane —H 4 MnO.->j These manganese oxides are usually sec¬ 
ondary in origin and occur frequently in residual clays, but they are not, 
however, of very widespread distribution. In clays they rarely exceed 
one per cent. They exert a coloring effect similar to that of iron and are 
often the coloring agents on those clays used in mineral paint or 
pigments. 
minerals in burned clay 
Very few attempts have been made to study the minerals in burned 
clay. Porcelain and some other types of high-grade products have 
been studied microscopically to some extent, but only about six investi¬ 
gators 1 seem to have carried on any experiments on clay alone. Somers 
apparently did the most exhaustive work so far attempted on American 
clays. 
Somers’ work shows that quartz usually stands out with much 
greater clearness in the burned than in the raw clay. He states that in a 
few cases a fluxing action appears to have taken place between the fine¬ 
grained material and the silica. 
iVernadsky, W., Soc. franc, mineralogie Bull., Vol. 13, p. 256, 1890. 
Glasenapp, M,, Ueber Aenderungen der Mikostruktur der Tone durch Ein- 
wirkung hoher Hitzegrade: Tonindustrie Zeitung, Vol. 31, p. 
1167, 1907. 
Klein, A. A., The Constitution and Microstructure of Porcelain: American 
Ceramic Soc. Trans., Vol. 18, p. 377, 1916. 
Mellor, J. W., Can the firing temperature of a body be determined from the 
microscopic appearance?: Eng. Ceramic Soc. Trans., Vol. 16, pt. 
1, p. 71, 1917. 
Somers, R. E., Microscopic Study of Clays, U. S. Geol. Survey, Bull. 709, p. 
300, 1922. 
Schurecht, H. G., The Microscopic Examination of the Mineral Constituents of 
some American Kaolins, Jour, of Am. Ceramic Society, Vol. 5, 
p. 3, 1922. 
