RoGEBRS. | Minerals of the Galena-Joplin District. 453 
Growth figures are seen on the face of the cube, consisting 
of depressions square in outline, the sides of the square being 
parallel to the diagonals of the cube face, as in figure4. The 
figure faces are parallel to the faces of the octahedron, and 
sometimes a bottom face is present. Occasionally the growth 
figures assume the form of projection, the fgure | faces being 
the same in both cases. 
Internal cavities were often observed, as shown in figure 5. 
These negative crystals are quite small and are bounded by 
the faces of the cube and the octahedron, though their inter- 
facial angles are usually much rounded. 
Composition.—The galena of the district is remarkably 
free from arsenic and antimony, the injurious elements so 
common in this mineral. Silver is usually present, though 
in very small amounts. Three samples from Joplin gave 
from 0.75 to 1.25 ounces to the ton. 
Here galena is one of the first minerals formed. Only the 
original chert, limestone, and, sometimes, dolomite, are of 
previous origin. The octahedral crystals of galena seem to 
be of later origin than the cubical ones. The former are often 
found on the latter in parallel position, and on other minerals 
formed subsequent to the cubic galena. In some cases, how- 
ever, it is of very recent origin. Old shovels and tools of 
various kinds are found in abandoned shafts or mines with 
small crystals of galena adhering to them. 
Galena is sometimes altered to cerussite, anglesite, pyro- 
morphite, leadhillite, and sulphur. Pseudomorphs of cerus- 
site, pyromorphite, and leadhillite, after galena, are known, 
the latter only from Granby. 
Sphalerite, or Zinc Blende; ‘‘JAack’’; ‘‘ BLACK JACK.”’ 
**‘Jack,’’ variously designated as ‘‘black jack,’’ ‘‘resin jack,’’ ‘‘steel 
jack,’’ etc. 
Composition, zinc sulphide, ZnS; zinc = 67 %, sulphur = 38 %; hardness, 
3°5-4; gravity, 3-9-4-1; color, commonly yellow, brown, black; also red, 
green to white, and, when pure, nearly colorless; crystallization, regular 
system; cleavage, dodecahedral, highly perfect. 
Observed forms: c{100! 00; p,{111!0,; d{110} 00; 
v { 12-1-1}12012; m,/311!—303 ; M,{833!—808; p}111!0; 
1}511}505; k,{17-6-6}— 12017; n,{322!— 808. 
