It is the only known mineral to contain thiocyanate ions, which are similar to cyanite but with oxygen in place of sulfur. Historically, thiocyanate was named rhodanide (Greek for “rose”) in honour of the red it makes when combined with iron. While rare in geology, thiocyanate is common in biology and you have it in your blood.

It is found in only one region, the Katanga Copperbelt formed when an ancient seabed was metamorphosed during continental collisions that ultimately formed the Gondwana supercontinent. The julienite deposit is part of a white talc schist formed by metamorphism of dolomite within the Katanga Copperbelt, which is the second largest copper reserve in the world and also home to massive sulfide ore deposits with significant amounts of cobalt, silver, nickel, bismuth and arsenic.

Julienite is named to honour Henri Julien, a geology graduate student who died while in the region collecting material for his dissertation. It’s unconfirmed but plausible that during his fieldwork he met Pierre Vanden Brande, who was on an unrelated expedition that discovered julienite about 10 kilometers to the south and who later suggested the name. Henri Julien was the son of Pierre-Alphonse Julien, the first professor of geology and mineralogy at the University of Clermont-Ferrand, and was an aspiring geologist in poor health when he died at 33 years old.

Transparent when clear, halite can take on a rainbow of hues depending on trace impurities by other elements, inclusions, or lattice defects in its crystal structure. Warm pink, orange, and yellow salts come from small amounts of iron oxide or organic impurities like bacteria or algae, while more striking blue and purple come from sodium nanoparticles or irradiation causing lattice defects. Because halite forms by evaporation of a brine, it often traps small amounts of liquids within it. These water pockets can be protected by the crystals for long periods of time, preserving evidence of past environments and even life.

Large deposits are a tectonic force capable of changing entire landscapes as salt domes rise like blobs in a lava lamp. This process happens through diapirism, where halite's low density and malleability squeezes it up through brittle overlaying sediment.

Along with its use as table salt, halite is also used as a food preservative by brining, dry curing, or fermentation. As a preservative, salt draws water out of food through osmosis, dehydrating it. High salt levels are toxic to many microbes (excluding salt-loving extremophiles called halophiles).