ANNUAL REPORT-MINERAL INDUSTRIES. 
31 
CLAY. 
The term clay is applied to earthy materials which pos¬ 
sess in a varying degree the property of plasticity, or 
stickiness when wet. Clay consists of a mixture of sev¬ 
eral minerals, rarely if ever of a single mineral. Hydrated 
aluminum silicate minerals, of which kaolinite is a type, 
predominate. With these is found quartz, feldspar, mica, 
iron, and many other minerals. The mineral particles 
are of varying size and are mixed in widely varying pro¬ 
portions. Chemically, the clays are both complex and 
variable. This follows as a necessary result of the vary¬ 
ing proportion in which the minerals occur. The physical 
properties differ as widely as do the mineralogical and 
chemical constituents. Thus in plasticity, clays vary from 
the remarkable plastic ball clays to slightly plastic kao¬ 
lins. In texture they may vary from the fine grained clay 
made up of particles of microscopic size to coarse grained 
clay grading into sands, sandstones and other rocks. 
Other properties as tensile strength, porosity, shrinkage, 
color, and fusibility depend upon the minerals present, 
the size of the particles, and the conditions in which they 
occur, all of which give rise to endless variations. 
Practical tests of clays must take into account chem¬ 
ical and mineralogical composition, and physical proper¬ 
ties. A chemical or ultimate analysis may serve to indi¬ 
cate certain properties of the clays. Thus if the total 
percentage of fluxing elements is high the clay may be 
expected to fuse easily. A mineral or rational analysis 
is intended to determine in so far as possible the min¬ 
erals present in the clay, and the relative proportion of 
each. Complete tests of the physical properties require 
specially adapted devices and machinery. 
The clays in Florida are among the promising unde¬ 
veloped resources of the State. The Survey plans contem¬ 
plate a thorough investigation of the clays of the State. 
The sandy clays suitable for road-making material will 
be investigated in connection with other road-making ma- 
