SECOND ANNUAL REPORT-MINERAL INDUSTRIES. 
247 
some distance along the eastern border of the Everglades north and 
south from Miami (see map). As in the case of the other limestone 
when first taken from the quarry it is relatively soft and easily 
worked, but hardens upon exposure. The hotel Halcyon .Hall and 
some other buildings at Miami are constructed of this rock. 
MATERIALS FOR MORTAR AND CONCRETE. 
Sands either siliceous or calcareous occur in practically all parts 
of Florida. Sands for mortar in order to give the best results should 
be angular in shape. This is due to the fact that a rough and angular 
sand grain permits a better bonding power than a smooth and spherical 
grain. The size of the sand grains also has a bearing on its qualities 
as a mortar sand. Coarse sand has a smaller surface area in propor¬ 
tion to volume than has fine sand. In order to obtain the best results 
each grain of sand in a mortar should be thoroughly coated with 
cement, and it appears probable that the coarse sand owing to its 
smaller proportion of surface area becomes better coated than a fine 
sand. While a coarse sand is preferable to a fine sand, for certain 
purposes it may be desirable to have a mixture of coarse and fine 
grains. The cement used in the mortar must be sufficient to completely 
fill all voids existing in the sand. The relative proportion of voids may 
be reduced by the use of a mixture of coarse and fine sands. Such a 
mixture of sands permits the use of a relatively smaller amount of 
cement, and is apparently without detriment to the resulting mortar. 
Sand is used along with lime in the manufacture of sandlime brick; 
and with cement in the preparation of artificial stone or building blocks. 
The sands most frequently used for mortar are siliceous. It ap¬ 
pears, however, from various tests that calcareous sands are in no way 
inferior. 1 In addition to the natural sands ground rock may also be 
used. A small amount of clay, not exceeding ten to thirty per cent., 
is said not to weaken the cement. The presence of humus or peaty 
matter, or an excess of clay as well as mineral particles of any kind 
subject to decay, must be guarded against. 
The illustrations of plate XV show the prevailing shape of the sand 
grains from a number of localities in Florida. The relative size of the 
sand grains is also indicated, all of the illustrations having been drawn 
to the same scale. 
The materials in Florida suitable for concrete consist chiefly of 
shell deposits and some compact limestones and of flint rock which 
may be crushed for the purpose. 
dement and Concrete, Sabin, p. 170, 1907. 
