294 A. F. Rogers— Delafossite. 



Cupric metaferrite, CuFe 2 4 , is known* but not its crystal 

 form. One would expect it to be isometric. 



Not many cuprous compounds are known, but they seem to 

 be related to alkali compounds rather than to the dyad metal 

 compounds. CuCl, CuBr, and Cul are isometric like the 

 sodium and potassium haloids. Sodium metaferrite, NaFe0 2 , 

 crystallizes in hexagonal plates and rhombohedral plates accord- 

 ing to van Bemmelen and Klobbie.f This compound and 

 delafossite are perhaps isomorphous. Chalcopyrite, CuFeS 9 , 

 analogous to CuFe0 2 , is tetragonal, but the sulpho-salts are 

 not usually isomorphous with the corresponding oxy-salts. 



Identity with Delafossite. — As the Bisbee mineral is a pure, 

 well-crystallized compound of definite chemical composition, it 

 is entitled to recognition as a distinct mineral species. It is 

 hexagonal-rhombohedral in crystallization and has the empirical 

 composition CuFe0 2 . It agrees with a Siberian mineral 

 described by Friedel under the name of delafossite except in 

 cleavage and hardness. As these properties are not funda- 

 mental the Bisbee mineral is referred to delafossite and the 

 evidence, it is believed, is complete enough to establish 

 delafossite as a definite independent mineral species. It is 

 probably cuprous metaferrite, Cu'Fe'^Og. 



Note. — Since writing the above Mr. Tovote has sent me 

 several additional specimens of delafossite from Bisbee. One 

 of them is a soft, black, graphite-like mineral which marks 

 paper and has a lamellar structure. It gives the same chem- 

 ical tests as the crystallized delafossite and agrees with the 

 description of the Siberian mineral. The lamellar structure 

 may account for the apparent cleavage and also for the inferior 

 hardness. Hematite presents an analogous case, for some vari- 

 eties are very soft and have an apparent cleavage in one direc- 

 tion which is due to lamellar structure. 



Stanford University in California, 

 November, 1912. 



*List, Berichte d. Deutsch. Chem, Ges., vol. xi, p. 1512, 1878. 

 f Jour, prakt. Chemie, vol. cliv, p. 509, 1892. 



