Benitoite is a rare and highly prized collector's gemstone famous for its intense blue color and strong blue fluorescence under short-wave UV light. It typically occurs as sharp, triangular dipyramidal crystals embedded in white natrolite veins within serpentinite. It is the official state gem of California, and the Dallas Gem Mine remains its only significant commercial locality.
Spotting benitoite in the field
Field marks- 1
Sapphire-blue triangular tabular crystals, usually small
- 2
Glows an intense chalky blue-white under shortwave ultraviolet light
- 3
Sits in white natrolite veins in blue-grey serpentinite
Benitoite is California's state gem and it is essentially a one-locality mineral: the Benitoite Gem Mine in San Benito County is the only place on Earth that has produced it in gem quality. The shortwave fluorescence is spectacular and is how the material is found, because a night sweep of the tailings makes the crystals blaze against the dark serpentinite. The site operates as a fee dig, and the practical method is to work the tailings with a UV lamp after dark.
Before you collect
Shortwave UV lamps damage eyes and skin. Wear rated eye protection during night collecting, which is the standard method here.
Straight answers
- Is it worth cutting?
- Facets beautifully, with dispersion higher than diamond, but it is soft for a ring stone and the rough is almost always small.
- What is it really worth?
- High, and constrained by the fact that there is only one source and it is largely worked out. Cut stones over a carat are genuinely rare.
- Can you legally keep it?
- Private claim operated as a fee dig, generally by appointment. There is no public land option.
Where it is worth going
- Benitoite Gem MineSan Benito County, California
The world's only significant benitoite locality. Fee dig, usually booked ahead, night UV collecting.
Often confused with
Benitoite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside benitoite
Minerals reported to co-occur with benitoite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- BaTiSi₃O₉
- Mohs hardness
- 6-6.5
- Density
- 3.65 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Hexagonal
- Crystal habit
- Triangular dipyramidal crystals
- Cleavage
- Poor on {1011}
- Fluorescence
- Blue under SW UV
- Rarity
- Rare
- Uses
- Gemstone, Collector
- Host rock
- In natrolite veins cutting glaucophane schist in a serpentine body (San Benito Co., California, USA); in a magnesio-riebeckite-quartz-phlogopite-albite dike cutting serpentinite (Ohmi, Japan)
Where rockhounds find benitoite
Classic worldwide localities
- Gem mine, Mina Numero Uno, the Victor and Junilla claims, and on Santa Rita Peak, San Benito Co., California, USA
- Big Creek-Rush Creek, Fresno Co., California, USA
- Trumbull Peak, near Incline, Mariposa Co., California, USA
- Diamond Jo quarry, Magnet Cove, Hot Spring Co., Arkansas, USA
- Ohmi, Niigata Prefecture, Japan
- Broken Hill, New South Wales, Australia
Field-hunting tip
Where it forms: In natrolite veins cutting glaucophane schist in a serpentine body (San Benito Co., California, USA); in a magnesio-riebeckite-quartz-phlogopite-albite dike cutting serpentinite (Ohmi, Japan). If you start seeing neptunite, joaquinite, natrolite in float, you are in the right ground. Typical habit: triangular dipyramidal crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify benitoite?+
Where is benitoite found?+
What rocks look like benitoite?+
What minerals are found with benitoite?+
What kind of rock does benitoite form in?+
What is benitoite used for?+
Find benitoite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
