RoGErs. | Minerals of the Galena-Joplin District. 473 
usually appearing as a single plane, or two, and rarely in its 
full number of three planes. 
g:, —2R, a very common form, is one to which several of 
the types owe their habit, among them 5, 13, and certain 
phases of type 4. As a subordinate form it truncates the 
shorter or acute polar edges of the common scalenohedron 
K:, +R*. Thus, its identification is as a rule very easy. 
The faces of this form are commonly cross-striated, and its 
combination edges with K: rounded, or even modified, by an 
undetermined scalenohedron of high indices. EKtch-figures 
of the form shown in figure 32 were observed on the faces of 
this form on crystals of type 2 from the Pittsburg mine, and 
of type 4 from the New Start mine, Granby. 
A4-, —iR was observed on crystals of type 19 from the 
Homestake mine at Granby, where it occurs as a subordinate 
form. 
9-, —4R was not identified by the writer. Farrington men- 
tions it as a prominent form on crystals of his type 5. 
&, —5R. Type 13, which includes crystals from the Home- 
stake mine at Granby, the Pelican mine at Joplin, and various 
mines at Aurora, has as its dominant form this rhombohe- 
dron in almost equal development with 9. 
x-, —11R is avery common form. On crystals of type 4 
(Farrington), which are found in almost every part of the 
district, and in great numbers, itis always present. Its usual 
pentagonal shape is shown in figures 37 and 38. It deter- 
mines the habit of crystals of type 8 from the Crystal Palace 
mine between Joplin and Central City. 
®, —14R is the dominant form on type 19, of which only 
a few crystals were seen. 
2., —2OR was not observed by the writer. It is mentioned 
by Farrington as occurring on twin crystals consisting of the 
forms K:, 8-, and g, where the twinning plane is S-. 
Nos. 23 to 25.—Scalenohedrons of the zone p §; this zone, 
a most important one among calcite crystals as a whole, is 
represented in our crystals by three scalenohedrons. 
