Duricrust is a hard crust (layer) found on the surface formed from mineral precipitation. Mineral precipitation is the deposition of insoluble materials from a solution. Minerals such as iron and aluminium are insoluble and when water (solution) evaporates, these minerals are left on or just below the surface where they compact and cement with other materials forming a hard layer. Duricrusts are very resistant to erosion and weathering and often cap hills or plateaus protecting the underlying soil or rocks from weathering agents.
Different insoluble minerals (metals or compunds) can form duricrusts and usually ends with "crete" such as:
Most duricrusts are mostly found in subtropical regions due to wet and dry periods present there. The wet periods allow soluble materials to be washed away in solution and subsequent dry periods allow more evaporation therefore precipitating (deposited) the insoluble materials. In arid regions, rapid evaporation causes minerals to precipitate creating resistant hill or plateau tops. Duricrusts containing more than one mineral or metal, for example iron and calcium is termed hardpan.