Gypsic horizons have significant accumulations of gypsum. Gypsum, or calcium sulfate, is a moderately soluble salt - more soluble than calcium carbonate but less soluble than sodium chloride. Gypsum may restrict soil use, both for agricultural and engineering purposes. In this magnified view of a thin section of a gypsic horizon seen under cross polarized light, white lenticular gypsum crystals fill much of the void system of the soil. The thin white surface layer of this soil is part of a salic horizon.
Salic horizons contain accumulations of salts more soluble than gypsum.
These horizons must have soluble salt concentrations of at lease 2 percent. Salts concentrate in salic horizons by capillary rise and evaporation from shallow groundwater tables. The most common salts in salic horizons are the chlorides and sulfates of sodium, calcium and magnesium. Cambic horizons are horizons in which minerals have been altered, removed or accumulated but not to the degree necessary to meet criteria for other diagnostic horizons. Petrocalcic horizons are cemented calcic horizons that are impenetrable by plant roots.