216 FLORIDA GEOLOGICAL SURVEY-I5TH ANNUAL REPORT

 CHAPTER IX


 SEDIMENTARY KAOLIN

 The Florida clay which has attracted the greatest attention, both from a commercial and a scientific point of view, is the "sedimentary kaolin", found at a number of localities in the central part of the peninsula. This clay is of interest to the ceramist and the clay operator because of its wide field of uses and peculiar characteristics, and to the geologist because of its unique occurrence, distribution and association with other materials. Much has already been written about this unusual clay with reference to its nature, origin and geologic age without these problems being definitely solved. Its physical properties and uses, however, are fairly -well known.

 TRMINOLOGY

 This clay has been va-iously known as ball-clay, china-clay, kaolin and plastic kaolin. It is commonly marketed under the name of plastic kaolin, or china-clay. The term china-clay is used broadly to include any white-burning clay, regardless of its origin. The term plastic kaolin is misleading in that it might include a residual deposit. The term kaolin is applied to a residual white-burning clay of high refractoriness and usually of low plasticity and bonding strength. A ball-clay is a plastic, sedimentary clay, white-burning, or nearly so, of high refractoriness, and usually good bonding strength.
 None of these terms, therefore, are entirely satisfactory, as in chemical and physical properties the Florida clay is intermediate between a true kaolin and a ball-clay. Its chemical composition is essentially that of washed kaolins from other regions and its alumina content ranges from three to seven per cent higher than is the case in the typical ball-clays. The Florida clay also has a much higher plasticity, shrinkage and bonding strength than the true kaolin. In occurrence, composition and properties it is very similar to the white coastal plain clays of Georgia and South Carolina, except that the Florida clays must always be washed before being used.
 The term "sedimentary kaolin" seems best suited for the white Florida clay, as this term shows the relationship to a true kaolin and