HIGH-GRADE SILICA MATERIALS 23 



Part 2 



ECONOMIC VALUE OF THE MATERIAL DESCRIBED 



High silica rock is used in the manufacture of glass, ferro-silicon, 

 carborundum, abrasives, silica brick, and tube mill liners and 

 pebbles ; quartz sand is used chiefly in the manufacture of glass of 

 various qualities. 



The availability of the rock used by these industries is in large 

 part dependent upon its composition and structure, and it is from 

 this point of view that the formations described will be referred to 

 the industries for which they seem best fitted. 



Manufacture of glass. Material used in the manufacture of glass 

 must be of uniform grain, of medium fineness (20 to 50 mesh), and 

 must contain, in general, not less than 98 per cent silica, and not 

 more than 0.25 per cent ferric oxide; sand of optical quality must 

 be of much greater purity than this,* however, and purer material is 

 also required in the making of flint and plate glass. 



Different writers are not in accord in their judgment of purity; 

 thus, Peddle * suggests five qualities of glass sand : ( i ) for common 

 work, not washed or sieved; Fe 2 O 3 o.io to 0.20 per cent; (2) for 

 common work, sieved, but not washed; particles larger than i mm 

 rejected, Fe 2 O 3 o.io to 0.20 per cent; (3) for ordinary colorless 

 glassware, plate and sheet glass ; washed and dried, but not graded ; 

 Fe 2 O 3 about 0.05 per cent; (4) for best crystal glass; washed and 

 sieved; Fe 2 O 3 about 0.04 per cent; (5) for work of highest class; 

 washed, dried and graded between 30 and 80 mesh; Fe 2 O 3 about 

 0.03 per cent. 



According to these requirements, glass sand may contain a maxi- 

 mum of 0.03 per cent Fe 2 O 3 and still be fit for the most exacting 

 work. Kummel and Gage, 2 however, place the allowable limit of 

 Fe 2 O 3 at less than o.oi per cent for ordinary glass, and from o.oi 

 to 0.02 per cent for common green bottle glass; the best flint glass 

 sand contained, according to analyses given, as little as 0.0017 per 

 cent Fe 2 O 3 . 



Meddle, C. J., British Glass-making Sands. I. Substitution of some 

 British sands for foreign sands in the manufacture of high-grade glass. 

 J. Soc. Glass Tech., i, 27-61. 1917. 



2 Kiimmel, Henry B M and Gage, R. B., Glass Sand Industry of New Jer- 

 sey; Report of State Geologist, 1906. 



