CLAYS OF NEW YORK Y81 



FIEE CLAYS 



Definition. Strictly speaking the term fire clay can be said to 

 include those clays which are able to withstand a high temperature. 

 Regarding the condition of the plasticity, the shrinkage in drying 

 and burning, the texture, and color, no fixed rules can. be laid 

 down; for, except in refractoriness, fire clays show a wide variation 

 in physical characters. 



Refractoriness. The degree of temperature which a fire clay 

 should be able to withstand without fusing has not been entirely 

 settled in this country, but in Europe, specially in Germany, a clay 

 is not considered refractory unless its fusing point lies above 

 2700° F. 



JSTevertheless many of the clays denominated fire clays which 

 are marketed in this country are not up to this standard, while 

 others are far above it. The color of fire clays varies, but they 

 are not infrequently colored bluish gray, gray or black by organic 

 matter. Some of those mined on Staten Island are pure white or 

 yellowish white, but at the same time they are highly refractory. 



Fire clays are divisible into two groups, the plastic, and the non- 

 plastic or flint clays. The former sometimes occur in the form 

 of hard shales which become plastic on grinding and mixing with 

 water, whereas no amount of grinding renders the fiint clays more 

 than very slightly plastic. The latter are not found in IsTew York 

 state, but occur abundantly in Pennsylvania, Ohio, Kentucky, 

 Missouri and one or two other states. 



In chemical composition the fiint clays stand close to kaolinite, 

 and at times even exceed it in the percentage of alumina which 

 they contain. (See Kaolin, p. 503.) Flint clays vary in color, 

 being gray, black, brown or even yellowish. The iron contents 

 of the bed are generally collected in concretionary masses. In 



