218 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
FLUORIDES. 
The almost universal presence of fluorite in vein fillings and as a metasomatic 
product in the rocks shows that the solution contained fluorine. The general char¬ 
acter of the solution indicates the presence either of calcic fluoride or of alkaline 
fluorides. 
Fluorite is by no means insoluble in pure water. According to the experi¬ 
ments of Wilson,® 1 part of calcium fluoride is soluble in 26,923 parts of H 2 0 at 15° C. 
It is stated 6 that it is more soluble in waters containing C0 2 , although exact figures 
are not given. It is thus less soluble than gypsum, of which 1 part dissolves at 
ordinary temperature in about 420 parts H,0, but considerably more soluable than 
barium sulphate, of which, it is stated, that 1 part is soluble in 429,700 parts H 2 0 
at +18° C. 
Under the influence of solutions containing alkaline carbonates fluorite alters 
to calcite, and this process is believed to be more or less active in the oxidized zone 
wherever the absence of pyrite permits the waters to be of an alkaline character. 
Fluorspar heated at 100° or 150° C. with solutions of sodium carbonate is 
easily converted to calcium carbonate, while sodium fluoride goes into solution 
(Sorby). This reaction takes place both at the elevated temperatures mentioned 
and at ordinary temperatures. Superheated water attacks fluorite and hydro¬ 
fluoric acid is formed. 
It is known that fluorine is contained in many thermal springs. The list of 
waters containing these constituents would no doubt be greatly extended if careful 
search were made for the element. Owing, however, to certain analytical difficul¬ 
ties it is rarely looked for. Fluorine has been shown to exist in the hot springs of 
Carlsbad, Plombii'res, Contrexeville, Chatenois (Alsace), Vichy, and Bourbon- 
l’Archambault. One of the waters at Vichy contains 0.00769 g. fluorine per liter, 
and that of Bourbon-1'Archambault 0.002689 g. per liter. c 
The- springs at Carlsbad and at Plombieres are known to deposit fluorite in 
small quantities. The latter springs, in fact, ascended on an old system of fissure 
veins, the gangue of which consists chiefly of quartz and fluorite. Fluorite some¬ 
times occurs closely associated with volcanic eruptions and is known especially 
from the volcanoes of Campania, Italy. The tuffs in this region are said to contain 
large masses of fluorite, which have probably been formed by the reaction of volcanic 
emanations containing fluorine upon the fragments of limestone. 
The two most important reactions concerning the formation of fluorite estab¬ 
lished by Bischof d are (1) the above-mentioned decomposition of fluorite by alkaline 
carbonates with the formation of calcite and alkaline fluorides, and (2) the decom¬ 
position of sodium fluoride in solution at ordinary temperature by calcium silicate 
with the formation of calcium fluoride. Bischof showed that ordinary rocks like 
basalt or trachytes, which contain some calcium silicate, had a like effect, but in 
less degree than the artificial silicate of lime. 
o Wilson, George, On the extent to which fluoride of calcium is soluble in water at 60° F.: Kept. Twentieth Meeting 
Brit. Assoc. Adv. Sci., 1S50, pt. 2, p. 69. 
i> Nickh'S, J., Recherches sur la diffusion du floor: Anal, de Chimie, 3d ser., vol. 53, 1858, p. 437. 
c Daubree, A., Les eaux souterraines k lYpoque actuelle, vol. 2, Paris, 1887, p. 9. 
d Bischof, G., Chemische Geologie, vol. 1, 2d ed., Bonn, 1863, pp. 48 and 54. 
