Guanajuatite is a rare bismuth selenide mineral typically found as metallic, lead-gray acicular or fibrous aggregates within hydrothermal veins. It is most famously associated with the mining district of Guanajuato, Mexico, where it was first discovered. Collectors prize it for its unique chemistry and metallic luster, though it is often brittle and requires careful handling.
Is this guanajuatite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch guanajuatite with a known reference. Guanajuatite sits at Mohs 2.5-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: shiny gray.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: lead gray, bluish gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular, crystalline, massive.
Often confused with
Guanajuatite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside guanajuatite
Minerals reported to co-occur with guanajuatite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Bi₂Se₃
- Mohs hardness
- 2.5-3
- Density
- 6.25-6.98 g/cm³
- Colors
- Streak
- Shiny gray
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular, crystalline, massive
- Cleavage
- Distinct on {010}, indistinct on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In hydrothermal deposits of low to medium temperatures
Where rockhounds find guanajuatite
Classic worldwide localities
- Salmon, Lemhi Co., Idaho, USA
- Thomas and Essex mines, Darwin, Inyo Co., California, USA
- Santa Catarina (type locality), La Industrial (type locality), and Nuestra Señora de la Luz mines, Sierra de Santa Rosa, near Guanajuato, Mexico
- Roter Bär mine, St. Andreasberg, Harz Mountains, Germany
- Falun, Kopparberg, Sweden
Field-hunting tip
Where it forms: In hydrothermal deposits of low to medium temperatures. If you start seeing bismuthinite, bismuth, clausthalite in float, you are in the right ground. Typical habit: acicular, crystalline, massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify guanajuatite?+
Where is guanajuatite found?+
Is guanajuatite safe to handle?+
What rocks look like guanajuatite?+
What minerals are found with guanajuatite?+
What kind of rock does guanajuatite form in?+
What is guanajuatite used for?+
Find guanajuatite on the map
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