60 THE AMERICAN MUSEUM. JOURNAL 
ACCESSIONS OF MINERALS. 
Some very unusual crystals of Stephanite, the sulphantimonite of 
silver, have been presented to the Museum collection by Edward L. 
Dufourcq, M. E. ‘These remarkably large and interesting crystals came 
from the Las Chispas Mine in Arizpe, State of Sonora, Mexico. ‘They 
have appeared but recently in collections, and probably all have come 
from this locality. ‘They seem to be developed in vugs, or cavities, under 
favorable conditions for crystallization. ‘Chey probably surpass in size 
any crystals of Stephanite previously known. ‘They are black, splen- 
dent, and twinned like aragonite, that is an orthorhombic crystal pre- 
sents a pseudo-hexagonal symmetry from interpenetration, twin lamelle 
being seen on the basal plane. ‘This species is hemimorphic (7. e. the 
opposite poles are dissimilar) but by supplementary twinning the termi- 
nations appear the same. ‘The find is undoubtedly of interest, and a 
crystallographic study of the crystals has already been made by Professor 
Moses of the School of Mines, Columbia University, of which Mr. Du- 
fourcq is a graduate. Although perhaps not appealing to the common 
eye, being black and involved groups, they will elicit very keen admira- 
tion from students and collectors. Accompanying this gift was a dona- 
tion from Mr. Dufourcq of seven well-crystallized and curiously rounded 
Argentite specimens, the sulphide of silver, and some very instructive 
examples of wire silver with Polybasite, another sulph-antimonite of 
silver. It has been often shown that heating silver sulphides with reduc- 
ing agents, as gas or even vapor of water, will reduce the silver sulphides 
to metallic threads. It would seem as if some such action had prevailed 
in the formation of the silver in these specimens. ‘The Stephanite 
specimens are like those from a neighboring mine that were described 
by Professor W. E. Ford in the March number of the American Journal 
of Science. 
Lo PSG 
