NATURAL SCIENCES OF PHILADELPHIA. 



307 



by the decolorization of the surface by a bronze tarnish and the occurrence in 

 the crevices of the blue Covelline (?). 



The crystals of Clayite do not appear to be in the least acted upon. Tn color 

 they are a blackish gray, are quite small, the form only to be distinguished by 

 a strong pocket lens, and no cleavage observed. Rubbed in an agate mortar, 

 they are quite malleable, though at first quite frangible. Streak black gray ; 

 sectile. Hardness about 2-5. 



Before the blow-pipe on charcoal it fuses easily, giving a yellow incrustation 

 surrounded by a white incrustation ; with carbonate of soda a strong alliaceous 

 odor, and a brilliant metallic globule when hot, which becomes dull and lustre- 

 less on cooling. 



The crystals, as before mentioned, coated a thin layer of quartz, on which 

 they were associated with small crystals of chalcopyrite. They were carefully 

 freed from all extraneous matter, and the analyses gave the following results : 



I. II. 



Sulphur, 8-22 per cent. 8-14 



Arsenic, 9-78 " 



Antimony, 6-54 



Lead, 68-51 



Copper, 7-67 



Silver, trace. 





67-40 

 5-62 



100-72 

 The less amounts of lead and copper in (II.) are to be accounted for by the 

 crystals taken for analysis having small particles of the amorphous portion ad- 

 hering. 



Per cent. 



Sulphur, 8-22 



Lead, 68-11 



Copper, 7-67 



Arsenic, 9-78 



Antimony, 6-54 



By taking 2 Cu = 1 Pb, we have the formula 



o 

 As 



Pb 



Cu 



Sb 



Owing to the partial decomposition of the amorphous portion, extending 

 generally through the specimen by the minute cracks and its minute quartz 

 granules, no positive composition can be assigned to it.* The following are the 

 results of a determination of the bases and a calculation of their ratio after the 



subtraction of the quartz : 



By calculation. 



Quartz, 25-73 per cent. 



Lead,.. 51-32 



Copper, 2-31 



Sulphur, 6-75 



(Antimony and Arsenic) loss 13-89 



100-00 



Per centage. 



Sulphur, 909 



Arsenic and Antimony,.. 18-69 



Copper,.. 3-11 



Lead,, 69-11 



100-00 



*The intimate mixture of quartz through the massive portion of the mineral gives it a 

 lighter color. 



1859.] 



