A. H. Chester—Mineralogical Notes. 289 
Other hemimorphie crystals of barite have been described by 
Reuss,* by Zepharovich,t and by Schrauf.{ These forms are 
all given in Schrauf’s Atlas, figs. 4, 12 and 15, under Baryt. 
The first two are hemimorphic in the direction of the same 
axis as the crystals from DeKalb, and the other in the line of 
the vertical axis. While all three are much more complicated 
than the simple one described here, none of them shows the 
face 2-2. 
The symbols used here correspond to the more common 
position of barite, where the plane of the principal cleavage is 
made the basal-pinacoid. The hemimorphism is better shown, 
as in fig. 2 above, by returning to the old system, still used by 
some authorities, where this plane is made the brachypinacoid, 
requiring of course a change of the symbols. 
7. PSEUDOMORPHS OF CERARGYRITE AFTER PYRARGYRITE. 
These interesting pseudomorphs were found among some 
‘ores and minerals from the Horn Silver Mine at Frisco, Utah, 
and are apparently not uncommon there. The matrix is 
sometimes a white amorphous silica, easily crumbled and con- | 
taining much water. It is evidently a variety of opal and 
clusely related to the geyserite of our Western hot springs. In 
other cases the matrix is nearly pure barite, always distinctly 
crystalline and occasionally seen in minute crystals. In color 
it is generally white or grayish, but occasionally it takes deh- 
cate lilac tints. Scattered somewhat sparsely through these 
two we find crystals of a dark color which grade all the way 
from pure pyrargyrite to pure cerargyrite. They are from 
2mm. to 4mm. in diameter and up to 10 mm. in length. 
Though rough externally they are easily seen to be in hex- 
agonal prisms and occasionally show rhombohedral termina- 
tions. 
Some of these crystals are found on examination to be pure 
unaltered pyrargyrite, consisting of sulphantimonide of silver 
with a little arsenic. Many of them are partially altered to 
cerargyrite, usually in an irregular manner, but occasionally 
are only altered on the outside leaving a core of pyrargyrite. 
Quite a number of them are completely changed and are 
chloride of silver throughout. This is then a case of pseudo- 
morphism by alteration and nota simple filling with chloride 
of silver of cavities left after the removal of pyrargyrite 
crystals. 
* Ber. Ak. Wien, lix, p. 623, 1869. + ‘‘ Lotos,” p. 8, 1870. 
$+ Ber. Ak. Wien, Ixiv, p. 199, 1871. 
