404 



[August 1 



100.22 

 This is a niccolite in which a small portion of the arsenic is replaced by 

 antimony and sulphur. 



XII. Artificial Alisonite (.?). 



About a year ago Mr. R. Pearce, Metallurgist of the "Works of the Bos- 

 ton and Colorado Smelting Co., at Argo, Colorado, kindly sent me some 

 very interesting crystals from furnace bottoms, which he had never before 

 deserved. 



They were octahedral crystals; some showed cubical planes and slight 

 indications of the dodecahedron ; they were mostly distorted, cavernous, 

 and many of them rounded, iron-black, and of metallic lustre. Spec, 

 gr. =5.545. Crystallized upon a plate of copper matte, containing a large 

 percentage of metallic copper. 



The analysis gave 



Calcu lilted. 

 17.61 



49.84 

 32.55 



100.00 



99. 



The composition is similar to alisonite or nearer 2PbS, 5CU2S in which 

 part of the copper is replaced by silver. The small percentage of sulphur 

 can be accounted for from a small admixture of metallic coi^iier, with 

 which some of the crystals were contaminated. 



University op Pennsylvania, August 17. 1882. 



