Around the turn of the 19th Century, a prospector discovered a blue material that he believed to be sapphire. Examination by experts determined the new gem material to be an unknown mineral. In addition, it turned out that the new material represented a previously unknown example of crystal form. It was given the name of benitoite, since it was found near the headwaters of the San Benito River in the county of the same name. Benitoite is prized for its adamantine, or diamond-like, luster and high dispersion. Its refractive index and dispersion are high enough to resemble colorless-to-blue diamonds. The fact that their specific gravity and hardness differs from that of diamonds, and that all benitoites fluoresce blue allows for differentiation. Benitoite was declared the official state gemstone of California. Although benitoites' public recognition and consequent desirability have increased dramatically over the past few years, supplies have not kept up with demand. Its only source was a small mine in San Benito County in northern California which is now closed. Most of the rough yields cut gems below ½ carat sizes. This rare and desirable gemstone is destined to become even more so. An oval-cut stone having a classic blue color, excellent clarity and luster of large size for the species. 

Bonhams. LAPIDARY WORKS OF ART, GEMSTONES AND MINERALS, 6 Dec 2017, 10:00 PST - LOS ANGELES