SEM morphologies of halite (NaCl) in soils

SUMMARY Halite (NaCl), the most common halide mineral, is omnipresent in saline soils and frequent in alkaline soils. The present study, with a scanning electron microscope, is undertaken to evaluate the morphologies of this mineral in soils and a recent sediment. Salorthids, from Iran and Syria, and a recent crust from the beach of a lake, are employed. The major part of the crust on the surface of the soil is composed of diffuse, waxy and massive forms of halite. The morphology is attributed to the hydroscopic nature of the salt which dissolves in its own absorbed water and crystallizes to give these forms. Directly on the crust surface is a layer of thin fibrous halite which shows elongation along the [100] axis. In the porous parts of the crust, secondary growths occur on the waxy and massive forms. The crystallites have a partially developed hexahedral habit and, according to their orientation, appear as cubes or as trigonal pyramids. In some cases the cubes grow along the axis normal to the surface, resulting in prismatic or acicular habits. In salic horizons the massive form is dominant. Euhedral forms only occur on the exposed face of the soil pit or on the pit floor. Perfect cubes—hexahedral—develop here.