AKT. 16. 



ANDORITE -BEARING SILVER ORE — SHANNON. 



The results in percentages of the essential constituents are below 

 recalculated to 100 per cent and compared with the theoretical per- 

 centages to suit the andorite formula : 



Original. 



Lead 23. 35 



Silver I 12. 09 



Antimony 37. 64 



Sulphur I 20. 08 



Total 93. 16 



Recalcu- 

 lated. 



25.06 

 12.98 

 40.41 

 21.55 



100. 00 



Theory. 



23.87 

 12.45 

 41.49 

 22.19 



100. 00 



This comparison shows that, while the mineral agrees in all 

 essential respects with andorite, it is slightly high in lead sulphide 

 and correspondingly low in silver and antimony. This may be due 

 to incipient alteration along the lines discussed below. 



The andorite gives, before the blowpipe, the usual reactions for 

 silver, lead, antimony, and sulphur. In the closed tube it decrepi- 

 tates slightly and fuses at a moderate temperature but without con- 

 spicuous decomposition, yielding faintly perceptible rings of sulphur 

 and antimony oxide, oxysulphide, and sulphide. In the open tube 

 it gives a copious sublimate of antimony oxide. The mineral is 

 soluble in hot concentrated hydrochloric acid. 



ALTERATION OF THE ANDORITE. 



While andorite was originally the most abundant metallic 

 mineral of the ore, typical unaltered andorite crystals are now rare, 

 the majority of the individuals being more or less affected by a 

 change which is first manifested by a granular appearance and 

 prismatic cleavage or parting. With further alteration a porous 

 core is developed in the andorite mass with a brilliant blue or purple 

 tarnish. In extreme stages of alteration the andorite contains a 

 central cavity filled with finely felted wool-like material or is re- 

 placed entirely by stellar aggregates of fine fibers. Partial analyses 

 indicate that crystals in the first stages of the alteration which have 

 been dulled in luster with the development of granular or sub- 

 fibrous appearance and prismatic parting do not differ greatly in 

 composition from the unaltered andorite. Two partial analyses of 

 materials showing these changes in properties gave the following 

 results : 



Analyses of partly altered a/ndorite. 



1. 2. 



Lead 25. 54 27. 86 



Silver ir 13. 35 12. 12 



Antimony 36.38 38.06 



