234 ECONOMIC GEOLOGY 



oxide falls below 30 per cent, it decreases at a far more rapid rate. 

 Ores carrying from 40 to 50 per cent, of the oxide are readily 

 marketable provided they are low in silicon. In spite of the 

 value of the metal in its numerous alloys and its wide application 

 in pigments the output is exceedingly small and most of the 

 ores are imported. 



