282 PROCEEDINGS OF THE ACADEMY OF [1886. 



posed of numerous prismatic crystals, the terminations broken 

 off sitting on well-crjstallized quartz, and from several smaller 

 specimens it would appear that quartz is the ordinary com- 

 panion of Stromeyerite at Zacatecas, whilst the other silver 

 minerals Proustite, Polybasite, Stephanite, Argentite are more 

 commonl}^ associated with Calcite. The faces of the crystals are 

 rough, not admitting close measurements ; the prismatic angle is 

 near r20-119. The mineral has no cleavage. Its fracture is 

 uneven to flat subchonchoidal and very splintery. The lustre 

 is brilliantly metallic and the color iron-gray with a strong bluish 

 purple admixture. The color of the powder is nearly the same. 

 It is not sectile, but mild, and has a hardness of 3, 5. 



Spec, gravity = 6*2303, made upon 1-623 grams of fragments 

 from several crystals. Before the blowpipe it melts verj"^ readily 

 to a globule, emitting sulfurdioxide, and changing to a gray 

 globule of silver-copper. Gives no sublimate on charcoal, nor 

 in open or closed tube, and dissolves in nitric acid to a blue solu- 

 tion, in which hydrochloric acid precipitates flocculent silver 

 chloride. 



A preliminary anal3'^sis made with a fragment from one cr3'^stal 

 (02346 gram) gave the result I ; a second analysis made upon 

 the mixed fragments used in the determination of specific gravity 

 (0"5 gr.) gave the result II. 



I. AgCl = 0-1615 ; Cu^S = 0-0958 ; BaSO, = 0-2837. 

 II. AgCl = 0-2509; Cu^S = 2105 ; BaSO^ = 0-5758. 



From this we calculate : 



Insoluble 



.d.1^ 



v/U. 



o 



100-97 99-94 



Analysis having been made with twice the quantity of sub- 

 stance and with greater care, deserves alone to be taken as basis 

 for the atomic ratio. Dividing the percentages by the atomic 

 weights, we obtain : 



Ag : Cu : S = 0-4661 : 0-5322 : 0-4975 

 Ag+ Cu : S = 0-9983 : 0-4975 

 = 2-007 : 1 

 Hence, 47 Ag^S + 53 Cu^S 



It is seen that Ag and Cu are not exactly in the ratio 1:1, 

 but very near. Undoubted Strome3'erite has been described 

 heretofore only from two localities, Schlangenberg, in Siberia, 

 and Rudelstadt, in Silesia, and from the latter place only in 



