Benitoite Benitoite is a rare blue silicate mineral, found in hydrothermally altered serpentinite. Benitoite fluoresces under short wave ultraviolet light, appearing light blue in color. Dr. Louderback, who conducted the discovery examination of this mineral, named it Benitoite, "as it occurs near the head waters of the San Benito River in San Benito County," California.