benitoite

{{Infobox mineral | name = Benitoite | category = Cyclosilicate | image = Benitoite HD.jpg | imagesize = 260px | caption = Benitoite on natrolite | formula = BaTiSi3O9 | IMAsymbol = Bni | strunz = 9.CA.05 | system = Hexagonal | class = Ditrigonal dipyramidal (m2) H-M symbol: ( m2) | symmetry = Pc2 | unit cell = a = 6.641, c = 9.7597(10) [Å]; Z = 2 | color = Blue, colorless | habit = Tabular dipyramidal crystals, granular | twinning = On {0001} by rotation | cleavage = [101] poor | fracture = Conchoidal | mohs = 6–6.5 | luster = Vitreous | refractive = nω = 1.756 – 1.757 nε = 1.802 – 1.804 | opticalprop = Uniaxial (+) | birefringence = δ = 0.046 | pleochroism = O = colorless; E = purple, indigo, greenish blue | dispersion = 0.036–0.046 | streak = White | gravity = 3.65 | melt = | fusibility = | diagnostic = | solubility = Insoluble: HCl, H2SO4 Soluble: HF | diaphaneity = Transparent to translucent | other = Blue fluorescence under SW UV; intense blue cathodoluminescence | references = }}

Benitoite () is a rare, blue, barium titanium cyclosilicate mineral, found in hydrothermally altered serpentinite. It forms in low-temperature, high-pressure environments typical of subduction zones at convergent plate boundaries. Benitoite fluoresces under short-wave ultraviolet light, appearing bright blue to bluish white in color. The more rarely seen clear to white benitoite crystals fluoresce red under long-wave UV light.