292 A. F. Rogers — Delafossite. 



delafossite from Bisbee is CuFe0 2 , which is equivalent to 

 Cu 2 O.Fe 2 3 , obtained for the Siberian mineral by Friedel. 

 Groth* gives the formula Cu" 2 0(Fe0 2 ) 2 on account of the 

 supposed analogy with ludwigite, Mg 2 0(Fe0 2 ) (B0 2 ). 



Chemical Constitution. — When we attempt to establish the 

 chemical constitution of the mineral there are serious diffi- 

 culties. The delafossite, it is safe to assume, is a copper salt 

 of an iron acid and not a mixture of copper and iron oxides. It- 

 may be cuprous metaferrite, Cu / Fe /// 2 , a salt of HFe0 2 , 

 (H 3 Fe0 3 -H 2 0), metaferrous acid, or a cupric salt (Cu^Fe^OJ 

 of H 2 Fe0 2 , a possible acid which we may call hypoferrous acid. 

 A number of metaferrites are known, but there is no record 

 of hypoferrites. 



Both the hydrochloric and sulphuric acid solutions of the 

 pure mineral give distinct tests for ferric and ferrous ions with 

 potassium ferrocyanide and potassium ferricyanide respectively. 

 These tests were made with coarsely crushed fragments of the 

 pure mineral free from hematite, so that the ferric iron test 

 was not due to oxidation by line grinding or to admixed 

 hematite. 



These tests indicate either that both ferrous and ferric iron 

 are originally present in the mineral or that in the act of solu- 

 tion a change in the valence of the iron takes place. The 

 compound Cu'Fe"'O a . Cu"Fe"O a or Cu 2 . CuO . FeO . Fe 2 3 

 also has the empirical formula CuFeO a and would account 

 for both the ferrous and ferric iron tests, but a formula of this 

 kind is very improbable. It is more reasonable to suppose that 

 a change of valence of iron has taken place during solution. 

 A few rough experiments by the writer confirm this idea. A 

 mixture of cupric sulphate and ferrous sulphate solution gives 

 a decided test for ferric iron. This recalls the blowpipe test 

 for ferrous iron.f 



Stokes:); gives the reaction : Cu /f +Fe"^=±Cu / + Fe / ", which 

 he established by experimental proof. The reversibility of 

 this reaction is also confirmed by experiments made by the 

 writer. Cuprous oxide and ferric oxide dissolve in sulphuric 

 acid to a green solution, which gives tests for both ferrous and 

 ferric iron. The reversibility of the reaction established by 

 Stokes explains why tests for both ferrous and ferric iron are 

 obtained from acid solutions of delafossite. 



We are still left in doubt as to whether the formula of 

 delafossite is CuTe^O, or Cu"Fe"0 9 . Either formula will 

 account for the observed facts. Mr. Bohart made a quantita- 



* Tabellarisehe Uebersicht der Mineralien, 4th ed., p. 79, 1898. 

 f A borax bead made blue with. CuO is changed in a neutral flame to opaque 

 red (Cu 2 0) by ferrous iron. The equation is : 2CuO + 2FeO = Cu 2 + Fe 2 3 . 

 % Bull. 186, U. S. Geological Survey, p. 44, 1900. 



