56 UNIVERSITY OF MISSOURI STUDIES 



pounds of galena in the old diggings which they are now search- 

 ing for barite. Very large masses of galena have been reported, 

 but even small masses are rare today. The galena always shows 

 evidence of attack by ground waters, and in fully half of the 

 specimens seen there was a layer of gray or white cerussite 

 around the galena. When it occurs in the clay it rarely shows 

 crystal faces, but, in the barite where it is protected from ground 

 water, crystal faces are retained. A bluish tarnish is a very 

 common feature of the galena found in the residual clays. The 

 cube modified by the octahedron is the predominating form of 

 crystal. Single crystals, five and six inches across, are found in 

 outlying districts where only a small amount of mining has been 

 done. Only a small amount of galena is found with the barite 

 in the veins. The galena is always later than the quartz and the 

 iron sulfides, and in all instances where it is found with sphal- 

 erite they are contemporaneous. 



Marcasite. — Marcasite, now largely changed to limonite and 

 hematite, is common in the district. As its determination is in 

 part dependent upon its crystal form, some marcasite may have 

 been mistaken for pyrite, which is more abundant. Marcasite is 

 found in fairly large masses in places. Fragments of what ap- 

 peared to be vein material weighing many pounds and covered 

 with marcasite crystals an inch or more in length, were found 

 on some of the steeper slopes. As noted above, most of the mar- 

 casite has been altered to limonite or hematite, but the crystal 

 form of marcasite has been perfectly preserved. Marcasite and 

 pyrite are found in the same deposit, but never immediately as- 

 sociated, so their relative age is unknown. Marcasite may 

 be older than the galena or sphalerite, but since crystals of it have 

 not been found associated with these minerals it is possible that 

 the marcasite is later than these minerals. It antedates the barite. 

 At the Eye mine marcasite was one of the latest minerals to be 

 deposited. 



Pyrite. — Pyrite, usually in well-developed crystals, is abund- 

 ant in the district. In the residual deposits it is altered, in large 

 part, to limonite and hematite. Many masses of limonite were 

 found which still contain a kernel of unaltered pyrite, and in the 

 veins the pyrite is usually unchanged. As a rule the pyrite lines 



