4:74 0. H. Warren — Alteration of Augite-llmenite Groups. 



is in fact generally evident from the relations of ilmenite to 

 the secondary silicates, that a very considerable portion of the 

 former has disappeared through reaction. It is to be par- 

 ticularly noted that leucoxenic alteration of the ilmenite is 

 absent in this type. Neither have the oxides of titanium 

 been observed to more than a trifling extent. The appearance 

 of characteristic aggregates of secondary hornblende and 

 biotite with residual ilmenite is shown in the accompanying 

 photograph. 



Summary of the mineralogical changes. — After the first 

 change of the augite to the fibrous (or compact) hornblende 

 there appears to have been a profound readjustment of the 

 various constituents of the hornblende, ilmenite and surround- 

 ing plagioclase, accompanied by recrystallization and more or 

 less transportation, possibly removal, of material. The par- 

 ticular chemico-mineralogic changes which may be noted here 

 1. The formation of a bine, soda-iron or soda-aluminiim 



are 



amphibole molecule from the soda (and alumina?) of the plagio- 

 clase and from the ferric iron of the ilmenite. The brown 





