458 University Geological Survey of Kansas. 
Here, then, we have an isometric crystal possessing apparent 
lower symmetry, namely, that of the rhombohedral-hemi- 
morphic class. Figure 11, an orthographic projection with 
| 111} as the plane of projection, represents a crystal of this 
habit. Truncating half of the dodecahedral edges are the 
faces of the tristetrahedron, M,{833|— 808. 
Twins are more common than the simple crystals. The 
twinning plane is the ordinary one for sphalerite, p | 111} O. 
As no reentrant angles are present the twins may easily be 
mistaken for simple crystals, but they may be recognized as 
such by the fact that the prominent dodecahedral faces have 
no other dodecahedral faces parallel to them, and by the fur- 
ther fact that in the positive octants only two of the M, faces 
are united at one point, while in the simple crystals three | 
meet around this point. The positive tetrahedron p occurs 
occasionally as a very subordinate form, though rarely it is 
quite large. Some other crystals of this type are quite dis- 
torted, often possessing apparent monoclinic or even a lower 
grade of symmetry. 
TypE 3. m,; 303; c,®O; y,12012; p, O. Crystals 
of this type are small, reddish ones occurring in cavities. 
They may be of secondary origin, representing the second 
generation of sphalerite. The dominant form is m,. The 
cube and the octahedron are subordinate forms with smooth 
and brilliant surfaces, while v, 12012, occurs in the zone be- 
tween them.. Twins are very frequent, indeed, and appear 
like simple crystals with one of the small m, faces, which are 
erouped together in a negative octant, truncated by a face of 
the tetragonal tristetrahedron, while in reality it is but a face 
of the cube in twinning position. Figure 11 represents one of 
these crystals untwinned. 
A crystal on which the dodecahedron is the dominant form 
with the positive tetrahedron as a subordinate form-was ob- 
served. As shown in figure 12, it is very symmetrical. It 
resembles a holohedral crystal more than any other I have 
seen, not excepting those composed of the two correlative 
tetrahedra. This crystal was obtained in the ore bin at the 
Owi mine, Galena. 
