124 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
rusty cracks and joints of weathered latite-phonolite. The mineral forms micro¬ 
scopic capillary crystals, which extinguish parallel with the prism axis and have 
very strong double refraction, the minute liair-like crystals giving interference 
colors of the third or fourth order. Chemical tests by Doctor Hillebrand show 
that the material is chiefly oxide of molybdenum and that the mineral is probably 
molybdite. 
A short distance east of the Howard flat vein the Ophelia tunnel crosses a small 
vein parallel to this and located on the Anaconda property. It consists of coarse 
quartz, with comb structure, growing on a black, fine-grained mixture of pyrite, 
molybdenite, and zinc blende with a very small amount of galena and traces of 
copper and tellurium (Hillebrand). Upon exposure to the sun and air the quartz 
turns yellow or green and finally a deep prussian-blue color. Specimens soon color 
the paper of the label to a similar blue. This energetic oxidation is also shown by 
little tufts of yellow material on the specimens and occasional coatings of a dark- 
blue mammillary substance. The yellowish material is believed to be molybdite 
or Mo0 3 . The blue substance, which dissolves in water and is associated with 
some ferrous sulphate, also contains a large amount of molybdenum and probably 
is the rare mineral ilsemannite (Mo0 2 , 4Mo0 3 ), which thus far has only been found 
at Bleiberg, Carinthia, as a product of decomposition of wulfenite, while it here 
appears as a direct product of oxidation of molybdenite. 
Calcite .—Calcium carbonate is fairly common in the district, usually as a 
product of alteration in basalts or other rocks containing much lime. Microscopic 
pseudomorphs of calcite after titanite are often seen in the latite-phonolites. In 
the veins it is, on the whole, uncommon. 
Dolomite .—A dolomitic carbonate of probably variable composition is common 
both as crusts in the veins and as the product of alteration in adjoining rock. It 
has in some cases the form of the primary rhombohedron and is often slightly 
greenish in color, probably due to copper. Qualitative analyses of specimens from 
the Last Dollar mine, where the mineral is especially abundant, showed lime, 
magnesia, iron, and manganese. Dolomite crystals, replaced by opal forming 
hollow pseudomorphs, were noted from the Orpha May mine. 
Rliodochrosite .—A pink carbonate, crystallizing in rhombic forms, from the 
Fluorine mine contains an abundance of manganese and is probably rliodochrosite. 
The same mineral is abundant in the Pointer vein in veinlets up to 3 or 4 inches in 
width, crystallized with fluorite, pyrite, galena, and sphalerite. It occurs also in 
similar association in the Lead vein of the Moon-Anchor mine. 
Barite .—Massive barite in considerable amounts has been reported from 
several mines on Globe Hill. The only occurrence of supposed barite in this 
vicinity which could be examined proved to be celestite, and much of the so-called 
barite is probably celestite. Barite is, however, definitely identified from some 
of the El Paso veins, and barium (probably as sulphate) has been determined by 
analyses in the Portland ores. A small vein containing green and purple fluorite 
with tabular barite crystals occurs in granite about 4 miles south-southwest of 
Cripple Creek, near the western brink of Cripple Creek Canyon. 
Celestite .—Our attention was first called to this mineral, which is a sulphate 
of strontium, by Mr. R. H. Burrows, who stated that it occurred in a vein crossing 
