benitoite

Benitoite is a rare blue barium titanium silicate mineral with the chemical formula BaTiSi3O9. It crystallizes in the hexagonal system and typically forms transparent to translucent prismatic or tabular crystals. The color is usually blue, though colorless to pale blue specimens occur. Benitoite has a vitreous luster, a Mohs hardness of 6–6.5, and a specific gravity around 3.65. It is notable for its strong blue fluorescence under shortwave ultraviolet light, a property that aids in identification and enhances its appeal to collectors and gem enthusiasts.

Occurrence and formation conditions are linked to ultramafic and serpentinite-hosted hydrothermal environments. The type locality is the Benitoite Mine in San Benito County, California, where it was first described in 1907 and where some of the finest gem material has been found. Benitoite is commonly associated with natrolite and other silicate minerals such as neptunite and joaquinite, reflecting its formation in complex, mineral-rich serpentinite settings.

Gem properties and uses: Benitoite is among the rare gemstones, prized for its vivid blue color and distinctive fluorescence. The rarity of gem-quality material means that high-grade crystals command significant value, and most supply has historically originated from California. California has designated Benitoite as the state gem, highlighting its cultural and geological significance.

Classification and naming: Benitoite belongs to silicate minerals containing barium and titanium, with the name derived from the San Benito County locality. It remains a widely studied mineral for its unique optical properties, rarity, and the geological context of its formation.