Dalnegroite is an extremely rare thallium-lead sulfosalt discovered in the skarn deposits of the Primorskiy Kray region in Russia. It typically occurs as small, lead-gray grains within complex sulfide-rich assemblages and is highly prized by advanced mineralogists for its unique composition.
Is this dalnegroite?
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 dalnegroite with a known reference. Dalnegroite sits at Mohs 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: brownish-red.
- 3Read the lusterHold the specimen under a strong light. Luster: submetallic.
- 4Match the color rangeCompare against the expected color range: dark gray.
- 5Look at form & habitCrystal system: triclinic. Typical habit: granular to massive.
Often confused with
Dalnegroite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Dalnegroite leaves brownish-red, Galena leaves lead-gray; luster reads submetallic on Dalnegroite and metallic on Galena.
How to tell apart: Streak differs, so Dalnegroite leaves brownish-red, Bournonite leaves steel-gray to iron-black; luster reads submetallic on Dalnegroite and brilliant to dull on Bournonite.
How to tell apart: Streak differs, so Dalnegroite leaves brownish-red, Sartorite leaves chocolate-brown; luster reads submetallic on Dalnegroite and metallic on Sartorite.
Often found alongside dalnegroite
Minerals reported to co-occur with dalnegroite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Tl₄Pb₂(As,Sb)₂₀S₃₄
- Mohs hardness
- 3-3.5
- Density
- 4.82 g/cm³
- Colors
- Streak
- Brownish-red
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Triclinic
- Crystal habit
- Granular to massive
- Cleavage
- None discernable
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Of hydrothermal origin in dolomitic marble
Where rockhounds find dalnegroite
Classic worldwide localities
- Lengenbach quarry, Binntal, Switzerland
Field-hunting tip
Where it forms: Of hydrothermal origin in dolomitic marble. If you start seeing realgar, pyrite, sb-rich hutchinsonite in float, you are in the right ground. Typical habit: granular to massive. Train your eye for that shape before scanning the outcrop.
Common questions
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Find dalnegroite on the map
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