a whitish layer of mineral salts, especially sodium sulfate, sodium chloride, and magnesium sulfate, often occurring on top of soils where rainfall is low.
refined soda ash.
refined sodium carbonate
any of several mineral salts, esp sodium sulphate, sodium chloride, and magnesium sulphate, that often appear on the surface of soils as a whitish layer in dry conditions
Collins English Dictionary - Complete & Unabridged 10th Edition
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Its distinctive aspect is the presence of occasional large grains of white alkali feldspar up to an inch long.
White alkali of the medium grade does not prevent the successful growing of asparagus.
Low lying sinks and the margin of playas are characterized by the presence white alkali and are virtually barren of vegetation.