No. 29: Sep-Oct 1993
"The nitrate deposits in the extremely arid Atacama Desert of northern Chile are among the most unusual of all mineral deposits. In fact, they are so extraordinary that, were it not for their existence, geologists could easily conclude that such deposits could not form in nature. The nitrate deposits consist of water-soluble saline minerals that occur as cement in unconsolidated surficial material -- alluvial fill in valleys, loose rocky debris on hillsides, and windblown silt and sand -- and as impregnations and veins in porous and fractured bedrock. They are found chiefly along the eastern side of the Coastal Range, but also within the Coastal Range, in the Central Valley to the East, and along the lower Andean front. Features of the deposits that appear to defy rational explanation are their restricted distribution in a desert characterized throughout by saline soil and salt-encrusted playas; the wide variety of topography where they occur; the abundance of nitrate minerals, which are scarce in other saline complexes; and the presence of other, less abundant minerals containing the ions of perchlorate, iodate, chromate, and dichromate which do not exist in any other saline complexes. Iodate,, chromate, and dichromate are known to form under such conditions, but no chemical process acting at temperatures and pressures found at the earth's surface is known to produce perchlorate."
(Ericksen, George E.; "The Chilean Nitrate Deposits," American Scientist, 71: 366, 1983.)
Reference. For more on these nitrate deposits and related phenomena, see ESP3 in our Catalog: Neglected Geologi cal Anomalies. Ordering information here.