454 University Geological Survey of Kansas. 
Sphalerite, the most important mineral of the district from 
an economic standpoint, is one of the most interesting from a 
mineralogical standpoint. Literature on its crystallography 
from this region amounts to practically nothing. 
The different forms will be described in detail : 
c/100}~mOx. The cube usually appears as rectangular 
faces truncating the interfacial angles of the negative tetra- 
hedron. On these faces are found slightly raised figures, 
oblong in shape, with rounded margins, the longer axis of 
the figure being parallel to the intersection edge of the cube 
with the negative tetrahedron. The cube faces usually show 
indistinct striations parallel to the above-mentioned intersec- 
tion edge. 
p, {111} O. The positive tetrahedron occurs as a small tri- 
angular or hexagonal face acuminating the solid angle of the 
negative tetrahedron or the rhombic dodecahedron. When 
unaffected by etching, the faces of this form exhibit smooth, 
lustrous surfaces. The process of etching gives rise to tri- 
angular etch-pits, and if this action proceeds far enough the 
smooth surface disappears, being replaced by very rough etch- 
hills. Figure 6 probably represents the etch-figures in their 
incipiency. ‘These may be described as three sets of very fine 
lines intersecting each other at angles of 120°, the lines ad- 
jacent the intersection of the tetrahedron with the cube being 
perpendicular to this intersection edge. 
p.{111/0,. The negative tetrahedron is very often the 
predominant form. Rarely smooth, it exhibits elevations of 
two kinds, the one irregular triangular elevations with two 
concave sides, the apex of the triangles pointing toward the 
intersection edge of the positive tetrahedron and the negative 
tetrahedron ; the other vacinal elevations modifying the in- 
tersection of the cube and the negative tetrahedron. 
d}110}e0O. The rhombic dodecahedron is usually not 
present, but on one type it is the predominant form. Asa 
rule, its faces are smooth, but occasionally it exhibits etch- 
figures. On one large twinned crystal these are developed to 
a remarkable degree. The etch-figures consist of etch-hills, 
which in plan appear as monosymmetric four-sided figures, 
