Cosalite is a lead-bismuth sulfide that typically forms distinct, elongated, needle-like or fibrous masses. Collectors often look for it within hydrothermal vein deposits where it manifests as radiating clusters or felted mats associated with other sulfide minerals.
Is this cosalite?
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 cosalite with a known reference. Cosalite 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: black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: gray, steel gray, silver white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: massive, radial.
Often confused with
Cosalite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Cosalite leaves black, Bismuthinite leaves lead-gray.
How to tell apart: Streak differs, so Cosalite leaves black, Galena leaves lead-gray.
How to tell apart: Streak differs, so Cosalite leaves black, Jamesonite leaves black. grayish.
Often found alongside cosalite
Minerals reported to co-occur with cosalite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb₂Bi₂S₅
- Mohs hardness
- 2.5-3
- Density
- 6.86-6.99 g/cm³
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Massive, radial
- Cleavage
- Very rare
- Rarity
- Uncommon
- Uses
- Collector, Ore of bismuth
- Host rock
- In hydrothermal deposits formed at medium temperatures but also found in contact metasomatic replacements, and epithermal replacements, as well as in pegmatites
Where rockhounds find cosalite
Classic worldwide localities
- Deer Park, Stevens Co., Washington, USA
- Red Mountain district, San Juan Co., Colorado, USA
- Magma mine, Superior, Pinal Co., and from Landsman Camp, Gila Co., Arizona, USA
- Darwin, Inyo Co., California, USA
- Nuestra Señora mine, Cosalá, Sinaloa, Mexico (type locality)
- Boston Creek, McElroy Township, and at Cobalt, Ontario, Canada
Field-hunting tip
Where it forms: In hydrothermal deposits formed at medium temperatures but also found in contact metasomatic replacements, and epithermal replacements, as well as in pegmatites. If you start seeing sphalerite, chalcopyrite, pyrite in float, you are in the right ground. Typical habit: massive, radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify cosalite?+
Where is cosalite found?+
Is cosalite safe to handle?+
What rocks look like cosalite?+
What minerals are found with cosalite?+
What kind of rock does cosalite form in?+
What is cosalite used for?+
Find cosalite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
