RoGERs. | Minerals of the Galena-Joplin District. 471 
from Aurora, 13 from Granby, Aurora, and Joplin, and 14 
from Granby, exhibit the form. 
Nos. 2 and 3.—Prisms. The prism of the first order, b, is 
a characteristic though subordinate form on crystals of type 
6, Nickel Plate mine, Aurora; type 15, Elizabeth mine, Jop- 
lin; type 20, Gracie Clarke mines, northwest of Galena. The 
prism of the second order, a, is sometimes observed on type 
20 as a narrow face truncating the basal or middle edges of 
the scalenohedron K:,+R’; also as a narrow face on type 17, 
from the Gracie Clarke mines. 
Nos. 4 to 9.—Positive Rhombohedrons. n-,+5R. This form 
is very common on the crystals of type 20, from the Gracie 
Clarke mines, Galena, and is frequently seen on other crystals, 
though it is never large. Its surface is rather rough. 
m-, +4R is avery common form. Rarely large, it is on 
crystals of type 22 the dominant form. Its characteristic 
deltoid shape is shown in figures — and —. [Etch-figures, 
as shown in figure 26, are very common on its faces. 
k- +3R is a very narrow form, truncating the obtuse polar 
edges of the scalenohedron K:, +R* on some of the crystals 
of type 10 from the John Jackson mine. 
p-, +R occurs very frequently, although it is not a common 
form for most other localities. On several of the types, 6, 7, 
and 12, it is the dominant form. As the cleavage rhombo- 
hedron it is a great aid in orienting the crystals. Faces of 
this form are often dull, and etch-figures are of frequent oc- 
currence. ‘These are deltoids, with their longer sides parallel 
to the polar edges of the faces, as figure 27 shows. They are 
often arranged in lines following the direction of their longest 
edges. Another form of etch-pits is shown in figure 28. 
e-, +2R was observed on but one type of crystals, 14, from 
the Mascot mine, Granby. It is not sharply differentiated 
from d-, +R. 
d-, ++R is a very rare form, occurring on crystals of type 
14, Granby, and type 16, Aurora. It is identified by the fact 
that it truncates the polar edges of 0-, —:R. 
