RoaeErs. | Minerals of the Galena-Joplin District. 455 
figure 7 with the axis of symmetry bd parallel to the shorter 
diagonal of the faces dodecahedron. Approximate measure- 
ments of the angles abc and adc gave 80° and 110°, respect- 
ively. The solid angle at b is elevated above the general 
surface of the crystal, while the points a, c and d are on this 
surface. In elevation, therefore, the etch-hills appear as in 
figure 8. The edges ab and be and the solid angle at b are 
modified by minute faces which are not represented in the 
drawing. The figure-faces abd and bed are highly polished. 
The etch-figures resemble those described by Becke,* except 
that the lines corresponding to ab and bc in figure 4 are 
parallel to the edges of the dodecahedron, while the lines in 
our figure are inclined about 20° thereto. And, further, the 
acute angles of the etch-figures of Becke’s crystals point to- 
ward the negative octant, while in ours they point towards 
the positive octant, or what we take for the positive octant, 
on account of the character of the surface of the tetrahedron 
appearing in the octant. 
v;12-1-1}|12012. This form is common on type 3, where 
it appears as a small, narrow face in the zone of the cube and 
the positive tetrahedron. The angle v,~c was measured un- 
der the cross-hairs of a microscope, with the following results : 
vac 12-1-1-,100, 17 measurements, average, 6° 56’, calcu- 
lated 6° 434’. 
1{511{505. This form was observed on but a single crys- 
tal in the same zone as the last above-mentioned form. The 
faces are smooth and exhibit nothing specially worthy of 
mention. The contact goniometer was used for the identifi- 
cation of the form, with these results: 
Ijc 511,100, 6 measurements, average 16° 00’, calculated 
15° 473’. 
m,{311}—308. This form, so common for sphalerite in 
most localities, is a very frequent one in the sphalerite crys- 
tals of the district, being the dominant form on type 3, which 
is of frequent occurrence. 
k,{17.6-6'—1,7017, This form, new for sphalerite, was 
4, Becke: Tschermak’s Min. u. Petr. Mitth., vol, v. p, 457, 1883, 
