The only source of this rare combination occurres at San Benito, California. They are formed in fractures of a serpentine rock from hydrothermal solutions. These solutions contained a number of unusual elements such as barium, titanium, fluorine, iron, cesium, niobium, manganese and lithium in relatively high concentrations. How such a solution occured and what other conditions caused the crystallization of these rare minerals is still not well understood. The rare clusters of blue benitoite and black neptunite on top of a crust of white natrolite produces a truly fantastic and a one of a kind mineral combination that is a must have for a serious mineral collector.
Color is typically blue, but also colorless and yellowish.
Luster is vitreous. Transparency crystals are transparent to translucent. Also found as small grains. Cleavage is absent. Fracture is irregular.