PHYSICAL SETTING OF CHILEAN BORATE DEPOSITS 767 
considerably in different parts of the area. The boron, however, 
occurs almost entirely as a single compound, the mineral ulexite, 
or boronatrocalcite (NaCaB,O,.8H.O). But there would seem to 
be in operation some process by which the various salts derived 
from the volcanoes are separated before being deposited on the 
lake flats, for in some parts of the field the boronatrocalcite occurs 
remarkably pure. It is in such places that it is now being worked 
for borax. The material is so free from other salts that it is only 
Fic. 2.—Borax incrusted lake flat with the volcano Ollagiie in the distance. 
Other volcanic peaks to the right. 
necessary to dry it before shipping it to Europe, where it is later 
refined. But in other parts of the region the borate occurs in beds 
alternating with layers of salt and salty earth with some glauberite 
and gypsum associated. 
Some distance beyond Cellobar is another dazzling white bed 
of borax whose flatness the railroad to Bolivia utilizes by running 
straight across it. Close by is the big volcano Ollagiie which is 
still smoking (Fig. 2). On other sides the borax flat is hemmed 
