F. A. Genth — Contributions to Mineralogy. 401 



Art. XLVL— Contributions to Mineralogy, J\ T o. 51; by 



F. A. Genth. 



1. Agidlarite, a new species. 



A precious lot of about half a dozen specimens, secured by 

 Mr. William Mven of Geo. L. English & Co., from Sefior 

 Aguilar, the superintendent of the San Carlos Mine at Guana- 

 juato, Mexico, as Naumannite, were placed in my hands for 

 identification. They all proved to be a new species which has 

 been named Agidlarite, in acknowledgment to the discoverer 

 of this interesting mineral. I am indebted to Messrs. Geo. L. 

 English & Co. for allowing me to break off a sufficient quan- 

 tity of this valuable material for investigation. 



There was only one piece in the lot which gave aguilarite in 

 a state of perfect purity. It is, associated with little quartz, 

 imbedded in colorless calcite which was readily removed by 

 dilute acetic acid. The pure crystals, thus obtained, were 

 placed in the hands of Prof. S. L. Penfield, who very kindly 

 determined the crystallization, of which he gives the following 

 description : 



"It is isometric; the crystals are skeleton dodecahedrons with 

 only the edges well developed. Many are lengthened out in the 

 direction of one of the crystallographic axes, looking then like 

 a tetragonal prism, terminated by a pyramid of the opposite 

 order; others are elongated in the direction of an octahedral 

 axis and these resemble hexagonal prisms, terminated by a rhom- 

 bohedron. I detached one crystal for measurement; it gave only 

 approximate reflections; eight dodecahedral angles, in three dif- 

 ferent zones, gave angles which varied between 60° 33 ; and 59° 

 35', the average being 60° 5', calculated 60° 0'. I also measured 

 two angles over the top of the dodecahedron 89° 59' and 90° 11', 

 calculated 90° 0'. The crystals are attached and grouped to- 

 gether, so that distinct, fully developed dodecahedrons do not 

 seem to occur." 



The largest crystals were not over 10 mm X 6 mm in size, groups 

 of crystals up to lo mm . No cleavage observed ; fracture hackly ; 

 sectile ; malleable ; H. = 2*5 ; sp. gr. = 7"586 ; color iron black ; 

 luster very brilliant. In an open tube at low heat, gradually 

 increased to red heat, it yields metallic silver, a slight sub- 

 limate of selenium, slender silky needles of selenous oxide and 

 sulphuric oxide, which latter, attacking silver, forms a small 

 quantity of Ag 2 S0 4 ; no Se0 3 could be observed. The analyses 

 gave : 



