A PRELIMINARY REPORT ON CLAYS OF FLoRIDA 77

 Hornblende-This is a complex silicate frequently found in some impure clays. It weathers readily and colors the clay red, owing probably 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.
 Vivianite-Fe3P20S, SH20. 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-MnO2 {
 Psilomelane-H4MnO.5 These manganese oxides are usually secondary 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 investigators' 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 finegrained material and the silica.

 lVernadsky, W., Soc. franc, mineralogie Bull., Vol. 13, p. 256, 1890.
 Glasenapp, M., Ueber Aenderungen der Mikostruktur der Tone durch Einwirkung 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.