schaller: the rutile group 177 



In conclusion, the author wishes to express his indebtedness 

 to Drs. J. L. Crenshaw and John Johnston, and Mr. Esper Larsen, 

 in collaboration with whom the experimental data for this article 

 were worked out; and to Dr. F. L. Ransome and W. H. Emmons, 

 and especially to W. Lindgren, for geological data. 



MINERALOGY. — A study of the rutile group. Waldemar T. 

 Schaller. To appear in a bulletin, " Mineralogical Notes, 

 Series II." of the U. S. Geological Survey. 



A theoretical study is made of the minerals comprising the rutile 

 group — rutile, cassiterite, mossite, tapiolite, nigrine, iserite, ainal- 

 ite, ilmenorutile and struverite. It is shown that they are all 

 either members or mixtures of members of a group of "primary 

 compounds", of which there are six chief ones, namely, ferrous 

 columbate Fe(Cb0 3 ) 2 , ferrous tantalate Fe(Ta0 3 ) 2 , ferrous tit- 

 anate Fe(Ti0 3 ), titanyl titanate (TiO)(Ti0 3 ), stannyl stannate 

 (SnO)(Sn0 3 ) and ferrous stannate Fe(Sn0 3 ). A study of all 

 the available analyses of these minerals proves the validity of the 

 assumptions made and it is concluded that of these minerals only 

 three, tapiolite, rutile and cassiterite, are definite species. Ilmen- 

 orutile (and struverite from Italy) is an isomorphous mixture of 

 compounds, in which iron, tantalum, columbium, and titanium 

 are present in quantity; struverite from South Dakota is a col- 

 umbic ilmenorutile; mossite is a columbic tapiolite; nigrine and 

 iserite are ferrous rutiles; ainalite is tantalic cassiterite; and the 

 various cassiterites from Mexico are ferrous cassiterites, arsenical 

 cassiterites, etc. 



