Mance: Quarry Industry of Southern Indiana 177 



In this formula x and y are variable quantities depending on the 

 relative proportions of silica and alumnia in the clay used. 



The essential ingredients of Portland cement may vary slightl}^ 

 in their chemical composition, but the hmits of variation are 

 reasonabh^ well marked. The average composition of the raw 

 materials is shown in the following table (Thorp, Outlines of In- 

 dustrial Chemistry, p. 184) : 





Clay 



Marl 



Lime- 

 stone 



Shale 



SiOo 



42 . 20 



0.50 



3.00 



15.00 



AI2O3 



12.30 



0.20 



1 1.50 



7.00 



FesOa 



4.60 



0.10 





CaCOo 



23.90 



94.50 



96.50 



71.00 



MgCOs 



16.05 



2.25 



3.00 



4.00 



Alkahes, moisture, etc 



0.95 



2.45 













It will be accurate enough to state that the mixture from which 

 Portland cement is made must contain approximately 75 per cent 

 of calcium carbonate, 20 per cent of silica^ alumina, and iron 

 taken together, while the remaining 5 per cent includes the 

 magnesia, sulphur, and other substances that are present as 

 impurities in the raw materials. 



It is seldom possible in nature to find a rock deposit approach- 

 ing the necessar}^ composition for the making of Portland cement, 

 so that the materials have to be derived from different deposits 

 and mixed as used. The usual ingredients for the manufacture 

 of Portland cement are obtained from deposits of limestone 

 which supply the calcium carbonate, and deposits of shale which 

 furnish the silica, alumina, and iron. 



Factors Determining Development. The factors that 

 determine the value of a deposit of limestone for the manufacture 

 of Portland cement are as follows: (1) chemical composition of 

 the material, (2) physical character of the material, (3) amount 

 of the material available, (4) location of the deposit of limestone 

 with respect to deposits of the other ingredients, (5) location of 

 the deposits with regard to transportation routes, (6) location of 

 the deposits with regard to location of fuel supply, (7) location 

 of the markets to be supplied. 



When considering the possibilities of turning the waste rock 



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