BAIN.] GANOUE MINERALS. 37 



tainod, and many very i)erfect ones adorn local cabinets. In the 

 veins a ribbon strnctnre giving the appearance of onyx is occasionally 

 seen. This seems to be dependent upon the distribution of coloring 

 matter. In general the spar is white, l)ut purple, amethyst, green, 

 and golden yellow are also jiresent, in the order of abundance given. 

 The cause of the color was not investigated. JVIr. Tangier Smith, 

 from his studies of the Kentucky fluorspar, concluded that the dif- 

 ferences in color were determined l)_y the condition of tlie coloring- 

 matter, pi'ol)al)ly hydrocarbons, i)i-esent. 



The fluorspar is almost univei'sally known by the shortened name of 

 spar, and the clear trans])ai'ent vai'ieties are known as glass spar. No 

 fluorine minerals other than llu()rs[)ar were found in the region, 

 except that in the dike rocks (here are unusual quantities of apatite 

 and. mica, both of which usually c(Mitain fluorite. 



CaTcite. — The most universal accompaniment of the fluorspar is 

 calcite or calcium carbonate, Ca(X).,. corresponding to 50 per cent of 

 calcium oxide and 14 per cent of carbon dioxide (specific gravity, 2.71 

 to 2.72). 



This mineral in its impure form constitutes the larger ])art of the 

 limestones of the region and also occurs in the shales and some of the 

 sandstones. It is the connnon cementing material where the rocks 

 have been l)recciated or fractured, and occurs alone forming impor- 

 tant veins, as well as with the fluorite. It is commonly not transparent 

 and rarely occurs showing crystal form, though the usual scaleno- 

 hedra with rhombohedral teruiinations occur. The mineral is not 

 itself valuable. It is locally considered an indication of the presence 

 of fluorite and the ore minerals, but occurs so commonly without them 

 that it is of small value in this particular. Calcite is fre(|uently 

 referred to locally as ^ calc.'' 



Quart-:. — In connection with tlu^ mineralization of the veins, large 

 quantities of silica, SiO., have been added to that already present in 

 the sandstones and other rocks. This silica has been dei)osited espe- 

 cially between the grains of sand of the original sandstones ah)ng the 

 veins, firndy cementing the rock and giving rise to the quartzite reefs 

 already mentioned. In druses in the vein and elsewhere the silica 

 has also cr3^stallized, forming small pyramidal crystals, some trans- 

 parent and others jet black. 



Barite. — Somewhat widely distributed but in relatively smaller 

 quantity than the minerals enumerated above is barite, the barium 

 sulphate, BaSO^ (.specific gravity, 1.3 to l.C)). This occurs as a mas- 

 sive, wdiite, crystalline substance intimately intergrown with the 

 other minerals. Occasionally on the free surfaces of druses it shows 

 crystal form, small tabular crystals clustered so a^i to form mammil- 

 lary aggregations being characteristic. In this it resembles the barite 

 occurring in southeastern Missouri. The larger clear cr^^stals, such as 



