CHEMICAL ANALYSIS OF BLUE HALITE

Potash mines in The Delaware Basin in southeastern New Mexico have rare occurrences of blue halite. These odd patches of halite are deposited within the upper Permian McNutt member of the Salado Formation. Late Permian glaciation periodically cut off the Delaware Basin from open marine waters which created an evaporitic environment. As sea level continued to drop, salt concentrations increased and halite and potassium-rich salts were deposited along the margins of the basin. As evaporation continued, the basin grew smaller into a ‘starved basin’. A similar geologic setting occurs in similar stratigraphic sequences in potash mines in Poland, Germany and Iran where blue halite has been observed.

Coloration of the halite varies from brown to amber, dark blue to light blue, and violet, but the cause of the coloration is not clear. One theory is crystallographic defects. F-center crystallographic defects allow a vacancy to absorb light in the visible spectrum which may cause the color change. It has also been suggested that radiation from potassium-40 can result in excess free sodium metal in the mineral. Colloidal gold has been found in higher concentrations which could also be the cause of the blue coloration.

Experimentally, X-ray diffraction of single crystals of halite illustrate that no excess sodium metal is present in the atomic makeup of the cubic structure. A ‘phantom density’ was observed in the center of the cubic structure, which may indicate a trace element. Further experiments are planned using X-ray photoelectron spectroscopy to determine the origin of the density. Fluorescence Spectrophotometer indicates normal readings of blue halite compared to clear halite. Observations of blue halite under artificial light can cause the disappearance of some color or change in color, similar to the effect of powdering the halite. Recrystallization of dissolved blue halite causes no reoccurrence of the blue color. Additionally, the stratigraphic occurrence of the blue halite within the potassium mine will be further investigated in order to determine the relationship between potassium and blue halite.