4 PROCEEDINGS OF THE NATIONAL MUSEUM. yol. 60. 



The only noteworthy change is a slight increase in the relative 

 amount of lead, which apparently increases gradually as the altera- 

 tion proceeds. The end product of the alteration is the fine fibrous 

 material which is present in small amount in pure form. One com- 

 pletely altered crystal was carefully analyzed, although there way 

 only 0.0771 grams of the material for analysis. This yielded the 

 following composition: 



Analysis of completely altered andoj-ite. 



Lead 45.14 



Iron 2.72 



Zinc 1. 56 



Silver 7. 78 



Antimony 23.22 



Sulphur (calculated) 19. 58 



Total 100.00 



This analysis yields the following ratios: 

 Ratios of altered andorite. 



Lead 0.2178 | 



Iron .0487 i 0.2904 1.04 x S 



Zinc .0239 ) 



Silver .0721 .0721 1.03 x 2 



Antimony .1932 .1932 .93 x 6 



Sulphur .6105 .6105 .97 x 18 



Unfortunately, the homogeneity of the small amount of material 

 analyzed was not demonstrable. Assuming that the above analysis 

 represents a homogeneous mineral, the formula yielded by the 



ratios is: 



8 (Pb,FeZn) S.AgoS.SSb^Sg. 



Separating Fe plus Zn from lead, this becomes: 



6PbS.2(Fe,Zn)S.Ag2S.3Sb2S8, or 

 Pb3(Fe.Zn)AgSb,S,. 



Such a formula would fall in the 3 :1 division of Foshag and 

 Wherry and in the bournonite group. However, since iron and zinc 

 were rejected as extraneous constituents of the original andorite, it 

 seems reasonable to likewise reject them here, the formula then 

 becoming : 



GPbS.Ag^S.SSb^Ss or PbgAgSbaSs- 



This formula falls in the 7 :3 division, diaphorite group of Wherry 

 and Foshag. While it is probable that a new mineral is here repre- 

 sented, the evidence does not justify the assigning of a new name. A 

 comparison of the last given formula with that of the unaltered 

 andorite brings out the fact that in the process of alteration the ratio 

 of silver to antimony has not changed, while the relative amount of 



I 



