238 PAIGE AND steiger: sericitization 



age of fluorine in the sericite is practically 0.20. Any lesser 

 amount of sericite would show a higher content of fluorine in the 

 sericite than that calculated. Equivalent silica was allotted to 

 the alkalies and the alkaline earths and the remainder computed 

 as quartz. The failure to sum up to' 100 per cent is due to water 

 in the sericite, not determined. 



When the fact is taken into consideration that sericite is a very 

 abundant mineral in the rocks of the T^yrone district, the amount 

 of fluorine indicated to be present in the district becomes very 

 significant; first in the role it must have played in the primary 

 mineralizing waters, for it is an element of great potency in 

 effecting the decomposition of aluminum silicates, and second, 

 its part in further decomposing the rocks during processes of 

 secondary enrichment on being set free by the action of sulphate 

 waters on sericite. 



That fluorine is potent to decompose aluminum silicates is 

 evident not only from the fact that it is used in ordinary analytical 

 work for this purpose, but its use forms the basis of several pat- 

 ents involving the decomposition of feldspar or kaolin. The 

 Doremus process of making potassium sulphate^ involves the 

 treatment of "finely powdered orthoclase with aqueous hydro- 

 fluoric acid." A soluble and an insoluble compound are pro- 

 duced. Both are further treated with sulphuric acid; sulphates 

 are obtained and the fluorine gas and acid recovered. 



The Childs process of deriving alumina from kaolin involves 

 the passing of hydrofluoric acid gas, or some other volatile com- 

 pound of fluorine, for example, silicon fluoride, through kaolin.^ 



It is well known that dilute sulphuric acid solutions will de- 

 compose sericite and that kaolin or kaolin-like products originate 

 from this reaction. Fluorine will be set free. 



The action of fluorine in descending solutions, whether derived 

 from fluorite or from sericite, might well be somewhat as follows: 

 Fluorite is decomposed by sulphuric acid with the formation of 

 calcium sulphate (CaS04) and hydrogen fluoride (HF) and 

 hydrogen fluoride unites readily with silica to form water and 



5 United States Patent Office, Spec'ficat on of letters patent No. 1,054,518, 

 patented February 25, 1913. 



« Patents Nos. 1,036,453 and 1,036,454, dated August 20, 1912 



