80 



KELLER— NOTES ON CHILEAN COPPER MINERALS. [April 24, 



similar to those of the Remolinos occurrence. The mineral is mas- 

 sive and amorphous, has a conchoidal fracture, a bluish-black color 

 and a liver-brown streak. Its hardness is between 3 and 4, and 

 the specific gravity 3.683 (instead of 2.5-2.6). When broken into 

 small pieces and carefully picked with the aid of a lens, the material 

 appeared quite homogeneous except for a few particles of quartz 

 and some green or bluish specks of a copper compound on the out- 

 side and along the crevices. A qualitative analysis showed that it 

 contains the oxides of manganese, copper and iron, together with 

 water and varying amounts of admixed silica. To ascertain whether 

 the mineral has a definite chemical composition analyses were made 

 of carefully selected samples from different specimens. It was 

 found that the silica, which separates on dissolving the substance 

 in hydrochloric acid, is not uniformly distributed through the mass. 

 Its percentage varied from 12 per cent, to 32 per cent., and its 

 microscopic examination showed that it consists entirely of quartz. 

 There could be no doubt, then, that it is simply an admixture, and 

 that in calculating the composition, the silica (of which only a trace 

 dissolves with the mineral) should first be deducted from the 

 amount of the substance taken. The results of the analyses were 

 as follows : 



Oxygen 



Manganous oxide 



Cupric oxide 



Cobalt oxide 



Barium oxide 



Ferric oxide 



Alumina.. 



Water 



I 



14.37% 



69.61 



5-86 



.48 



•36 



2.05 



1.92 



5.14 



99.79% 



II. 



14.18% 

 68.95 

 6.05 

 .56 



.47 



1.94 



1. 91 



_5-29 



99-35% 



III. 



13-89% 

 69.44 



5-69 



not det. 



not det. 



1.89 



2.10 



IV. 



not det. 



70.61% 



6.48 



not det. 



not det. 



4.22 



It is seen from these figures that the proportions of the several 

 constituents of the mineral are fairly constant. The composition is 

 that of psilomelane, in which part of the manganese is replaced by 

 copper. It is difficult to account for the very constant proportions 

 of oxide of iron and alumina. 



Regarding the determinations of water and of available oxygen, 

 I mav mention that the former was made bv heating the substance 



