Benjaminite is a rare silver-lead-bismuth sulfosalt that is typically found as small, lead-gray metallic grains within hydrothermal vein deposits. It is often challenging to identify in the field and usually requires microscopic analysis or X-ray diffraction to distinguish from other complex sulfide minerals. Collectors prize it as a rare example of silver-bismuth mineralization often found in association with other sulfosalts.
Is this benjaminite?
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 benjaminite with a known reference. Benjaminite sits at Mohs 3.3-3.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic, with greasy appearance.
- 4Match the color rangeCompare against the expected color range: grayish yellow, copper.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive, granular, or fine-grained lamellar aggregates.
Often confused with
Benjaminite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Benjaminite is noticeably harder (Mohs 3.3-3.5 vs. 2.5-2.75); streak differs, so Benjaminite leaves black, Galena leaves lead-gray.
How to tell apart: Benjaminite is noticeably harder (Mohs 3.3-3.5 vs. 2-2.5); streak differs, so Benjaminite leaves black, Aikinite leaves grayish black.
How to tell apart: Benjaminite is noticeably harder (Mohs 3.3-3.5 vs. 2.5); streak differs, so Benjaminite leaves black, Matildite leaves pale gray.
Often found alongside benjaminite
Minerals reported to co-occur with benjaminite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ag₃Bi₇S₁₂
- Mohs hardness
- 3.3-3.5
- Density
- 6.7 g/cm³
- Colors
- Grayish yellowCopper
- Streak
- Black
- Luster
- Metallic, with greasy appearance
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Massive, granular, or fine-grained lamellar aggregates
- Cleavage
- Fair, parallel to the elongation
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a quartz vein near the contact of a soda-granite and an intrusive rhyolite (Outlaw mine, Nevada); with arsenides (Camsell River, Canada); in a veinlet in calcite (Cobalt, Canada)
Where rockhounds find benjaminite
Classic worldwide localities
- Outlaw mine, about 17 km north of Manhattan, Round Mountain district, Nye Co., Nevada (type locality), USA
- Alaska mine, Poughkeepsie Gulch, near Ouray, San Juan Co., Colorado, USA
- Terra Company mine, Camsell River, Northwest Territories, Canada
- Canadian Keely mine, Cobalt, Ontario, Canada
- Porvenir mine, Cerro Bonete, Potosí, Bolivia
- Pirquitas deposit, Riconada Department, Jujuy Province, Argentina
Field-hunting tip
Where it forms: In a quartz vein near the contact of a soda-granite and an intrusive rhyolite (Outlaw mine, Nevada); with arsenides (Camsell River, Canada); in a veinlet in calcite (Cobalt, Canada). If you start seeing aikinite, chalcopyrite, pyrite in float, you are in the right ground. Typical habit: massive, granular, or fine-grained lamellar aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
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Find benjaminite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
