60 UNIVERSITY OF MISSOURI STUDIES 



diggings in the district. In no instance does it amount to more 

 than a bit of evidence that some copper is present in the deposit. 



Smithsonite. — Smithsonite in waxy botryoidal crusts on 

 sphalerite, barite, and dolomite is quite common in those deposits 

 which contain sphalerite. The crusts are seldom more than one- 

 eighth of an inch thick. Smithsonite is especially abundant in 

 the zinc mines near Fletcher, Missouri. 



Cerussite. — Cerussite is often found as a thin white to gray 

 coating on galena. This is especially true where the galena is still 

 in close association with the dolomite. 



Silicates 



Kaolin is the only silicate that occurs with the deposits. 



Kaolin. — Kaolin is, of course, the chief constituent of the 

 clay and is of various shades of red and yellow from the iron 

 oxides. Nearer the surface it is black or gray from organic mat- 

 ter. It is very plastic and shows an exceptional shrinkage on 

 drying. It cracks irregularly with a conchoidal fracture. De- 

 posits 20 feet thick are found in some localities. 



Sulfates 



Barite is the only sulphate found in the district. 



Barite. — Barite is the most important mineral in the district. 

 It will be described very fully because of its great importance. 

 It has the following compositions: BaS04; S03=34.3% and 

 BaO=65.7%. It crystallizes in the orthorhombic system. The 

 usual forms are tabular crystals parallel to the base and bounded 

 by a short prism on the sides. Crystals were found which show 

 both the macrodomes and the brachydomes in combination with 

 the above. On some crystals a series of these domes was recog- 

 nized. The crystals are elongated parallel to the brachyaxis or 

 to the macroaxis. Some of those collected are simple and per- 

 fect, while others are very complex. 



The usual form of the barite is in crested, divergent groups 

 of tabular, curved crystals. This is known as crested barite. 

 (PI. Ill, D and PI. IV, A and B.) These crested masses are often 

 six or eight inches long, with crests extending from end to end. 

 In other instances there are large concretion-like or cone-shaped 



