472 University Geological Survey of Kansas. 
Nos. 10 to 23.—Negative Rhombehedrons. These forms are 
highly characteristic for the region, and on many of the types 
are the dominant forms. The steep ones and the low ones 
are about equally represented. 
D-, —zR usually appears as a very narrow face between o 
and 6-, though sometimes it is quite large when 2: is lacking. 
Crystals with this form are from Aurora and from the Mascot 
and Homestake mines, Granby. Types 18, 14, and 16. 
6-, —zR is perhaps the commonest of the rhombohedrons, 
rivaling g-, —2R in this particular. While rarely dominant, 
it is very important in determining the character of the ex- 
tremities of many of the crystals. On a modification of type 
4 from the Pelican mine itis the dominant form, while it is 
the only form present on a few crystals found at the Portland 
mine, Leadville hollow, Joplin, which are designated as type 
21. Striations parallel to the edge, p-/0- are very frequently 
present. On one crystal the faces of this form have etch- 
figures, as shown in figure 29. 
7, —4R usually occurs with 4, and is especially common 
on crystals of types 2, 8, and 20. Rib-like striations, shown 
in figure 30, are characteristic of it. 
ke, —R. Though not common, this is a frequent form on 
crystals of a rhombohedral or low scalenohedral aspect, as 
types 12 and 15, from the Big Six and Elizabeth mines, re- 
spectively. On the latter itis a prominent form. Its faces 
are rough, being marked by deltoid etch-pits or growth 
figures. 
4., —8R is a characteristic form on the crystals of type 
9 from the Blaikie No. 2 mine. The faces are deltoid in 
shape, with deep etch-pits of the outline in figure 31. 
p>, —&R was observed on several crystals of type 2 from the 
Pittsburg mine, Joplin. | 
v-» —5R is a prominent, sometimes the dominant, form on 
crystals of type 24. 
m, —R is a form frequently noticed on crystals of type 4. 
As Farrington has observed, itis of quite sporadic occurrence, 
