48 
FLORIDA GEOLOGICAL SURVEY. 
Siliceous Rocks :—Flint and Chert. 
Flint is chemically an oxide of silica Si0 2 with more 
or less accompanying impurities. It is a variety of the 
mineral quartz, occurring massive and non-crystallized or 
more accurately very imperfectly crystallized (crypto¬ 
cry staline). The term chert is often used interchangeably 
with flint. Properly chert is an impure flint or flinty rock. 
Flint and chert are lacking in cleavage. They break, as 
do the other varieties of quartz, with conchoidal fracture. 
A flint rock when crushed breaks into sharp cornered 
pieces of varying size. 
Properties:—The mineral quartz, of which flint is a 
variety, has a hardness of seven on a scale in which the 
hardest mineral diamond, is ten. The varieties of quartz 
vary in hardness slightly according to the impurities that 
they contain. Silica is one of the least soluble of min¬ 
erals and among the most resistant to decay. 
Occurrence of Flint and Chert in Florida :—Flint and 
chert occur mostly as masses or “horsebacks” in the lime¬ 
stone formations. A good illustration of the manner of 
occurrence may be seen in phosphate pits or in some of 
the pits of the Florida Lime Co., at Ocala. In some of the 
sinks on Thompson’s farm two miles east of Suinterville 
will be seen flint masses exposed by the natural decay of 
the limestone. The flint masses appear to conform to no 
rule as to size and extent. A flint may form a ridge run¬ 
ning through the limestone; or again they occur as 
rounded or elongate masses. Occasionally the flint forms 
as a thin stratum lying horizontally. This flint bearing 
limestone lies at no great distance from the surface 
throughout all of the central peninsular section of the 
State from Columbia County on the north to Sumter 
County on the south and from the Suwannee River and 
the Gulf coast to east Alachua and Marion Counties. 
Much of the hard rock phosphate rests upon and in this 
flint-bearing limestone, and from the phosphate pits great 
quantities of the flint may be obtained. Occasional flint 
