Rogers. | Minerals of the Galena-Joplin District. 463 
Chalcopyrite. 
Composition, copper and iron sulphide, CuFeS2; copper—34:5%, iron= 
30-5%, sulphur=35%; hardness, 3-5-4; gravity, 4-1-4-3; color, brass yel- 
low; crystallization, tetragonal system. 
Observed forms: c{O001}OP; z{111}P; m{100} oPo. 
Chalcopyrite is a widely distributed mineral in the district, 
but never occurs in large quantities. ‘The crystals are tetrag- 
onal sphenoids with a tetrahedrid aspect, as shown in figures 
16 and 17. | 
As a.rule, the unit sphenoid z occurs alone, and it is al- 
ways the dominant form. Rarely the edge z,jz' is truncated 
by the basal plane c. This plane is always rough, and is 
frequently striated parallel to its intersection edge with z, or 
at other times the striations are perpendicular to those just 
mentioned. The faces of the sphenoid z are striated parallel 
to the edge c,z, or perpendicular to this edge. One face 
shows both of these striations, one on the lower part of the 
face, the other on the upper. The form m, prism of the 
second order, occurs as a narrow face truncating the polar 
edges of z. Its surface is smooth. 
Chalcopyrite occurs on sphalerite as small crystals arranged 
in parallel position, so that reflection from their surfaces is 
obtained at the same time. ‘There seems, however, to be no 
definite relation between the chalcopyrite and the sphalerite. 
Chalcopyrite seems to be the one original copper mineral 
from which all the other copper minerals of the district have 
been derived. It alters to limonite, cuprite, malachite, and 
chalcanthite. A red, blue or purple tarnish on its surface is 
very common. Pseudomorphs of limonite after chalcopyrite 
are found at the Jeanie mine, Galena. 
Pyrite; ‘‘MUNDIC”’ in part. 
Composition, iron disulphide, FeS2; iron=46-6%, sulphur=53-4%; hard- 
ness, 6-6-5; gravity, 4-95-5-10; color, pale brass yellow; crystallization, 
regular system. 
Observed forms: c}100!»Om; p{111}0O; £{410} 004; 
2{720!00%; {210} Q2. 
The cube occurs alone, its faces often being much distorted 
and curved. Striations are very common on its faces, due 
