Benitoite

Benitoite is a very rare mineral containing barium, titanium and silicon. It is known for its tones from sapphire blue to colourless and for a dispersion of light that in some directions exceeds that of diamond. Its gem-quality crystals have been produced in commercial quantities only from a single mine in the US state of California, so faceted stones are few and most are smaller than one carat. California made benitoite its official state gem in 1985.

Jewellery: Benitoite is cut as a faceted stone and used in rings and pendants. Because it has no distinct cleavage, it is easy to facet. But it is sensitive to sudden temperature changes and to ultrasonic vibration, so it should not be cleaned in an ultrasonic cleaner. Collecting: Blue crystals on white natrolite are among the most sought-after specimens for mineral collectors. Science: Because it fluoresces strongly under an electron beam, it is used in electron microprobes to adjust and align the beam size; it also serves as a standard in analyses for barium and titanium.

It has a hardness of 6–6.5 on the Mohs scale. It can scratch glass; a steel knife scratches it only with difficulty. Its specific gravity is 3.64–3.69 g/cm³.

Its best-known localities: Benitoite Gem mine (New Idria district), San Benito County, California, USA; Big Creek–Rush Creek area, Fresno County, California, USA; Trumbull Peak (near Incline), Mariposa County, California, USA; Magnet Cove (Diamond Jo quarry), Arkansas, USA; Ōmi, Itoigawa, Niigata Prefecture, Japan.

Its colour runs from sapphire blue to violetish blue; blue and colourless zones can appear together in one crystal. Pink and colourless stones are very rare. Its pleochroism is strong: looked at from one direction the crystal is blue or violetish blue, from another colourless. Its crystals are flattened, often triangular or hexagonal in outline, and are found in white natrolite together with rare minerals such as neptunite and joaquinite. Sapphire and tanzanite: it can be confused with them because of its similar blue colour; benitoite shows higher birefringence than sapphire.

On the “street to diamond” value ladder it sits on step 7 of nine: Precious stone. What matters most in benitoite is the saturation and evenness of the blue, clarity, cut and size; because the pleochroism is strong, cutting the stone in the right direction also matters. Because gem-quality material comes from a single mine, and according to GIA's 1997 study about 5,000 carats of faceted stones were produced over the life of the mine, supply is very limited; about 2% of those stones weigh over 2 carats. Pink and colourless stones are very rare, and the orange colour is produced by heat treatment. Because synthetic benitoite can be made, a laboratory report showing that a stone is natural is important.

Some stone sellers and crystal-therapy sites claim that benitoite is linked with the throat, third eye and crown chakras, supports spiritual communication and “astral travel”, gives protection, and even eases communication with beings from other worlds. There is no scientific evidence that benitoite has any effect on spiritual or extraterrestrial communication, protection or health; these claims come mostly from sellers' and crystal-therapy writing. The stone's real appeal is its rarity, its colour and its dispersion of light. This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.