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caliche

1. n. [Geology]
A crust of coarse sediments or weathered soil rich in calcium carbonate. It forms when lime-rich groundwater rises to the surface by capillary action and evaporates into a crumbly powder, forming a tough, indurated sheet called calcrete. Caliche typically occurs in desert or semi-arid areas. Of particular concern to geophysicists is the difficulty in acquiring good seismic data when shooting through a layer of caliche.
2. n. [Geology]
A deposit of sodium nitrate that is mined and used for fertilizer in parts of South America.