ZONAL WEATHERING OF A HORNBLENDE 



205 



represent (by weight) kaolin, 50 per cent; limonite, 25 per cent; 

 bauxite, 18 per cent; other substances, 7 per cent. It is highly 

 probable that part of the silica is present in some compound not 

 containing alumina, and if so the amount of bauxite is correspond- 

 ingly greater. This lends a distinctly bauxitic-lateritic aspect to 

 the alteration. 



Fig 4 — " Straight line diagram" showing changes in composition with alteration. 

 The full line represents analysis 2, the broken line analysis 3, compared with the 

 analysis of the fresh rock. 



TABLE III 

 Per cent-^-mol. wt. 



Specimens similar to the one studied are not uncommon in the 

 weathered part of the dikes, and the changes shown are believed 

 to be fairly typical for the rock in question. It is to be noted that 

 the fresh rock is much richer in iron than rocks which yield bauxite 

 deposits, and richer in alumina than those yielding high grade 

 laterite deposits. 



