THE NITRATE DEPOSITS OF CHILE 13 



and one containing 60 or 70 per cent, is very rare, though of course in 

 selected specimens even 90 per cent, or more of sodium nitrate may 

 be found. The impurities are sand, clay, gravel, and rock fragments, 

 with a very variable admixture of saline materials. The rock frag- 

 ments are similar to those already described in the costra, overlying 

 the nitrate. In some places they are scattered only sparingly through 

 the deposits; in others they are so numerous as to form a breccia 

 or conglomerate with the nitrate as a matrix. 



The saline impurities in the nitrate are mostly common salt (sodium 

 chloride) , with variable amounts of sodium sulphate (Glauber salts) 

 and calcium sulphate, the latter often occurring as crystalline gypsum 

 and perhaps also as anhydrite. In addition, there occur sodium 

 and calcium borates, as well as carbonate, chloride, and other salts of 

 calcium, and various salts of aluminum, magnesium, potassium, 

 ammonium, and a small but very constant quantity of sodium iodate. 

 Bromine compounds, together with other materials in small quanti- 

 ties, are sometimes, though more rarely, present. The common salt 

 (sodium chloride) occurs in varying amounts in all the nitrate deposits, 

 sometimes in very large quantities, and we find all gradations in admix- 

 ture from deposits composed mostly of nitrate to deposits composed 

 mostly of salt. The other saline materials are in comparatively 

 small amounts, though in special cases some of them may be more 

 abundant than the common salt. 



The following analyses represent the composition of samples 

 of crude nitrate (caliche) from different localities. The analyses 

 were made in Chile by Mr. D. G. Buchanan, chemist of the Alianza 

 Company, and were kindly sent to the writer by Mr. J. F. Comber, 

 manager of the North Lagunas Company. 



The saline impurities in the crude nitrate are generally purely 

 mechanical admixtures, like the salt, but sometimes they are associ- 

 ated with the nitrate in certain proportional relations, forming dis- 

 tinct minerals. Thus we have darapskite and nitroglauberite, both 

 minerals consisting of hydrous nitrates and sulphates of sodium. 

 Moreover, both the nitrogen and the iodine occur in small quantities 

 in other combinations than with sodium. Small amounts of potas- 

 sium nitrate are often found, while calcium nitrate (nitrocalcite) and 

 barium nitrate (nitrobarite) as well as calcium iodate (lautarite) and 



