464. University Geological Survey of Kansas. 
to oscillatory combination with the pyritohedron e. Solid 
angles of the cube are often acuminated by octahedron faces. 
The pyritohedron e occurs alone and in combination with the 
cube. Often the forms c, e, p and an undetermined diploid 
occur together on a crystal. 
Small crystals in black shale, from the Mastin ground, 
Galena, consist of the single form f{410} (fig. 18). The 
following measurements were made under the cross-hairs of a 
microscope, with these results: 
Average. Calculated. 
f,f 410,410 12 measurements, 27° 29’ 28° 44” 
The form e}720{ occurs as small. crystals in limestone at 
Galena. The following are the measurements on which the 
identification of the form was based (measurements being 
made under the cross-hairs of a microscope) : 
<a Average. Calculated. 
eae 120,720 5 measurements, 31° 48’ 31° 53) 
eae 720,720 6 6G 32° 18’ 31° 534 
In general, pyrite is far less abundant than marcasite, but 
in the Galena subdistrict it is more abundant. It alters to 
limonite, melanterite, and copiapite. Pseudomorphs of li- 
monite after pyrite are not uncommon. 
Mareasite ; ‘‘MUNDIC’’ in part. 
Composition, iron disulphide, FeSe; iron=46-6%, sulphur=53-4%; hard. 
ness, 6-6-5; gravity, 4-85-4-90; color, pale brown yellow; crystallization, 
orthorhombic system. 
Observed forms: p{001}OP; q{010}m>Po; m{110}oP; 
r{014}4P@; 2{012)4Po. 
The basal pinacoid p is striated parallel to its intersection 
edge with the brachypinacoid b. The unit prism is always 
horizontally striated, as is frequently the brachypinacoid b. 
Faces in the zone of brachydomes are much striated and 
often in oscillatory combination with each other. Perhaps 
other brachydomes than those given occur. The crystals are 
invariably flattened in the direction of the vertical axis. 
Four types of crystals may be distinguished : 
Typé 1. Rather large crystals in groups called ‘‘cocks- 
comb’’ pyrites. The forms present are p and m, the faces of 
