116 



ECONOMIC GEOLOGY 



iron and known by the miners as black jack. Calamine, the 

 hydrous silicate of zinc, and smithsonite, the carbonate of zinc, 

 appear as associated minerals. Both of these are classified in the 





 M 



c 

 3 

 o 



O 

 <u 



c 

 o 

 o 



trade as silicates. The lenticular, tabular and cylindrical forms 

 are more common in the southeastern and central districts than 

 in the southwestern. 



