- Chemistry: BaTiSi3O9, Barium Titanium Silicate.
- Class: Silicates
- Subclass: Cyclosilicates
- Uses: As a gemstone and as a mineral specimen
Benitoite is a somewhat obscure, but wonderful gemstone mineral that was only discovered at the beginning of this century. It has a sapphire blue color and was first thought to be a variety of sapphire. But x-ray studies showed that the crystal structure was unlike any mineral previously discovered. It is one of only a few minerals to crystallize in the bar 6 m 2 class called the ditrigonal-dipyramidal symmetry class. While this class is techically hexagonal, it produces trigonal (triangular) looking crystals. Additionally benitoite is also a fluorescent mineral. Nearly all specimens of benitoite will fluoresce a beautiful pale blue color under UV light (see above).
Benitoite is associated with a few rare minerals such as black-red neptunite, snow white natrolite and brown-yellow joaquinite. The only source of this rare combination occures at San Benito, California. They are formed in fractures of a serpentine rock from hydrothermal solutions. These solutions contained a number of unusual elements such as barium, titanium, fluorine, iron, cesium, niobium, manganese and lithium in relatively high concentrations. How such a solution occurred and what other conditions caused the crystallization of these rare minerals is still not well understood. The rare clusters of blue benitoite and black neptunite on top of a crust of white natrolite produces a truly fantastic and a one of a kind mineral combination that is a must have for a serious mineral collector.
- Color is typically blue, but also colorless and yellowish.
- Luster is vitreous.
- Transparency: Crystals are transparent to translucent.
- Crystal System is hexagonal; bar 6 m 2
- Crystal Habits include the flattened six faced dipyramid that has a distinct triangle shape often modified by minor faces. Also found as small grains.
- Cleavage is absent.
- Fracture is irregular.
- Hardness is 6 – 6.5
- Specific Gravity is approximately 3.6 (above average)
- Streak is white.
- Other Characteristics: Nearly all specimens fluoresce blue under UV light.
- Associated Minerals include serpentine, neptunite, natrolite, joaquinite, sanbornite, taramellite, albite and fresnoite.
- Notable Occurrences include only the mines of San Benito County, California, USA for good excellent crystals. SW Texas produces tiny grains in eocene sands as well as some other California localities.
- Best Field Indicators are crystal habit, fluorescence, color, associations and locality.