MINERAL INDUSTRIES LIME AND LIMESTONE. 57 



. Dcpusits of fossil shells arc likewise numerous, although as a rule 

 less free from impurities than are the accumulations of recent 

 shells. 



Compact and hard limestones are found at many localities in 

 the state, which when crushed afford desirable material for con- 

 crete. As stated under "Building" Stone" local areas of compact 

 and partly crystallized rock are found within the Vicksburg lime- 

 stone formation which lies near the surface over much of central 

 Florida. The Chattahoochee formation likewise has compact lime- 

 stone strata, and the rock of this formation is being mined at Live 

 Oak. The limestones of the Everglades which include strata that 

 will serve excellently for concrete have already been described. 



Flint is chemically an oxide of silicon (Si02), with more or 

 less accompanying" impurities. It is a variety of the mineral quartz, 

 occurring massive and non-crystallized or more accurately ^■ery im- 

 perfectly crystallized (cryptocrystalline). The term chert is often 

 used interchangeably with flint. Properly chert is an impure flint 

 or flint}^ 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 

 \arving 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 relatively insoluble minerals and is very resistant to decay. 



Occurrence of Flint and Chert in Florida : — Flint and chert 

 occur mostly as masses or "horsebacks" in the limestone forma- 

 tions. 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 Sumterville can be seen flint masses exposed by the 

 natural decay of the limestone. The flint masses appear to con- 

 form to no rule as to size and extent. They may fomi ridges 

 running through the limestone ; or again they may 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 Countv on the north to Sum- 



