20 



F. A. Cornfield — Mineralogical Notes. 



Art. III. — Mineralogical Notes', by F. A. Canfield. 



a 



It was the desire of the writer to have the late Professor 

 Pentield publish the following notes, as they are, in a way, 

 supplemental to the three papers published by him on the 

 respective subjects. As this is now impossible he feels obliged 

 to do it himself. 



I. Willemite. — In his paper on willemite.* 

 Professor Penfield illustrates in fig. 7 a crys- 

 tal with a tetartohedral termination. The 

 other end of the crystal was buried in the 

 matrix and could not be examined. By care- 

 fully removing the rock, this termination was 

 found to be of the common form, made up of 

 r and e planes in about the relative proportions 

 shown in fig. 1. 



As far as known to the writer, this is a 

 unique occurrence of a hemimorphic crystal 

 of willemite. This specimen was found in the 

 deep mines at Stirling Hill, 1ST. J., and not at 

 Franklin Furnace, as stated in the paper cited. 



II. Argyrodite. — In his paper on argyro- 

 dite^ Professor Penfield expressed regret at 

 the lack of knowledge as to the occurrence of 



• argyrodite in Bolivia. The writer first saw 

 this mineral in Potosi, in the winter of 1885-1886, but he was 

 unable to learn much about it except that it was very rich in 

 silver. It was impossible to obtain any specimens owing to 

 the pride of the owners in the possession of such rich ore. 

 It was only when financial distress, due to investments in 

 unprofitable mines, was felt, that the rare specimens could be 

 obtained. Argyrodite is always associated with the richest 

 silver ores, such as pyrargyrite, stephanite and native silver 

 and perhaps argentite, although this last mineral is quite as 

 rare as the argyrodite. The gangue is blende with perhaps a 

 little pyrite and siderite. This class of ore is found in quan- 

 tity only at Porco and Colquechaca. These towns are about 

 one hundred and twenty miles apart. The largest masses of 

 argyrodite were found at Porco. One piece weighs more than 

 five kilograms. The largest crystals were . also found there ; 

 one rhombic dodecahedron measures two and a half inches on 

 its axis. An octahedron modified by the rhombic dodecahe- 

 dron was shown to the writer in Porco. It measured about an 

 inch along its axis. Unfortunately this specimen was lost, its 



* This Journal, xlvii, 305. f IToid., xlvi, 107. 



