Benitoite is an extremely rare barium titanium silicate mineral named after San Benito County, California - the location where it was first found and described in 1907. There it occurs in a host rock of blue schist where the benitoite crystals formed in fractures from hydrothermal fluids. Benitoite is known to occur in just a few other locations worldwide. The Dallas Gem Mine in San Benito County is the only place in the world where gem-quality benitoite is found and where benitoite is found in specimen-quality crystals.
When cut as a gemstone, benitoite has an appearance and optical properties that are similar to sapphire. Most specimens are blue to violetish-blue, although a few rare orange specimens are known.
Description is credited to https://geology.com/gemstones/states/california.shtml#benitoite