Nuffieldite is a rare lead-copper-bismuth sulfosalt that typically occurs as fine acicular or fibrous crystals in hydrothermal ore deposits. It is best identified by its metallic lead-gray color and its specific mineral associations with other bismuth-rich species in localized mining districts.
Is this nuffieldite?
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 nuffieldite with a known reference. Nuffieldite sits at Mohs 3.5-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: dark greenish gray to black.
- 3Read the lusterHold the specimen under a strong light. Luster: bright metallic.
- 4Match the color rangeCompare against the expected color range: gray, steel gray, grayish green, reddish brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular, prismatic.
Often confused with
Nuffieldite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Nuffieldite is noticeably harder (Mohs 3.5-4 vs. 2-2.5); streak differs, so Nuffieldite leaves dark greenish gray to black, Aikinite leaves grayish black; luster reads bright metallic on Nuffieldite and metallic on Aikinite.
How to tell apart: Nuffieldite is noticeably harder (Mohs 3.5-4 vs. 2.5-2.75); streak differs, so Nuffieldite leaves dark greenish gray to black, Galena leaves lead-gray; luster reads bright metallic on Nuffieldite and metallic on Galena.
How to tell apart: Streak differs, so Nuffieldite leaves dark greenish gray to black, Bournonite leaves steel-gray to iron-black; luster reads bright metallic on Nuffieldite and brilliant to dull on Bournonite.
Often found alongside nuffieldite
Minerals reported to co-occur with nuffieldite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb₂Cu₁.₄(Pb₀.₄Bi₀.₄Sb₀.₂)Bi₂S₇
- Mohs hardness
- 3.5-4
- Density
- 7.01 g/cm³
- Streak
- Dark greenish gray to black
- Luster
- Bright metallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular, prismatic
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In vugs in a small quartz vein in the Lime Creek stock (Lime Creek deposit, Canada)
Where rockhounds find nuffieldite
Classic worldwide localities
- Alaska mine, Poughkeepsie Gulch, San Juan Co., Colorado, USA
- Patsy Creek, immediately south of the Lime Creek molybdenum deposit, Kitsault, near Alice Arm, British Columbia (type locality), and at Izok Lake, Northwest Territories, Canada
- Secu Valley, Baia Bora̧ district, Romania
- Spissko-Gemerske Ore Mountains, eastern Slovakia
- Les Houches, Haute-Savoie, France
- Maleevskoe, Rudnyi Altai, Russia
Field-hunting tip
Where it forms: In vugs in a small quartz vein in the Lime Creek stock (Lime Creek deposit, Canada). If you start seeing molybdenite, cosalite, aikinite in float, you are in the right ground. Typical habit: acicular, prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
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Find nuffieldite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
