38 FLUORSPAR DEPOSITS OF SOUTHERN ILLINOIS, [bull. 255. 



occur in southwestern Missouri, were not noted, though possibly pres- 

 ent. The mineral is locally known by the common name, heavy spar. 



Dolomite. — The double carbonate of magnesium and calcium, while 

 possibly present in occasional small quantities, was nowhere noted, 

 though Mr. Fobs has shown the writer the iron-manganese-magne- 

 sium-calcium carbonate, ankerite, from one of the Kentucky mines. 

 Dolomite is probably present, but only in very small quantity, a fact 

 of some possibh^ significance as related to the genesis of the ores. 



j{aoHu.—T\\Q hydrous sdicate of alumina (2H,0,Al.,0.„2SiOo) 

 occurs near the Pittsburg mine in considerable quantity. It does not 

 seem to be directly related to the ores, and its origin is in doubt. 



ORIGINAL INIETALLIC MINERALS. 



Qaleno.-^Tha sulphide of lead, PbS, containing 13.4 per cent of 

 sulphur and 86.6 per cent of lead (specific gravity, 7.6), is probably 

 the most abundant and widespread of the original metallic minerals. 

 It occurs in the usual cubical crystals, occasionally showing the faces 

 of both cube and octahedron. It is intimately associated with other 

 sulphides and with gangue minerals. The galena of this district is 

 argentiferous, at least to a degree notably beyond that of other de- 

 posits in the Mississippi Valley. Whitney " gives an assay showing 

 the presence of 9^ ounces of silver to the ton in galena from Rosi- 

 clare, and Eilers quotes the statement of the owners of the old Min- 

 eral City property to the effect that 8 to 14 ounces were commonly 

 found in the ore yielding 12 to 20 ounces in the pig. Whether this 

 amount is constant or not is uncertain, and no attempt has been made, 

 so far as is known, to save the silver, nor does its presence affect the 

 price of the lead. 



The lead ore now obtained comes mainly from the jigs employed to 

 clean the fiuoi-ite, and its production is incidental to the preparation 

 of the latter for the market. Large bodies of galena corresponding to 

 those formerly mined do not seem to be anywhere in sight at present. 



Blende.— T\\Q zinc sulphide, ZnS (sulphur, 33 per cent; zinc, 67 per 

 cent; specific gravity, 3.9 to 4.1), locally known as " jack," is, next to 

 galena, the most abundant of the sulphides. It occurs crystallized 

 but rarely wdth crystal form. The blende present is usually quite 

 pure, being a brown " rosin jack," and apparently rather free from 

 any admixture of pyrite. While many hand specimens and even 

 small quantities of ore can be found running high in blende, no 

 considerabk^ bodies rich enough to warrant independent mining were 

 exposed when the area was visited. At the Rosiclare mill middlings 

 containing zinc are being accumulated with a view to possible future 

 sale. 



"Whitney, J. D., Geol. Survey Illinois, vol. 1, 1866, p. 189. 



