Erniggliite is a highly rare thallium-tin-arsenic sulfosalt found almost exclusively in the famous Lengenbach Quarry of the Binn Valley. It typically occurs as tiny, metallic black tabular crystals embedded within dolomite or associated with other rare sulfosalt species. Due to its extreme rarity and toxicity, it is sought after primarily by advanced systematic mineral collectors.
Is this erniggliite?
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 erniggliite with a known reference. Erniggliite sits at Mohs 3.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Erniggliite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Erniggliite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: trigonal. Typical habit: tabular crystals.
Often confused with
Erniggliite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Erniggliite leaves black, Sartorite leaves chocolate-brown.
How to tell apart: Erniggliite is noticeably harder (Mohs 3.5 vs. 1.5-2); streak differs — Erniggliite leaves black, Hutchinsonite leaves red; luster reads metallic on Erniggliite and adamantine on Hutchinsonite.
Often found alongside erniggliite
Minerals reported to co-occur with erniggliite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Tl₂SnAs₂S₆
- Mohs hardness
- 3.5
- Density
- 4.74 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Tabular Crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Dolomitic Marble
- Typical price
- $200-1000+ for rare micro-specimens
Where rockhounds find erniggliite
Classic worldwide localities
- Lengenbach Quarry, Binn Valley, Switzerland
Field-hunting tip
Look in dolomitic marble country — that is the host setting where erniggliite typically forms. If you start seeing realgar, sartorite, hutchinsonite in float, you are in the right ground. Field specimens usually show a tabular crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify erniggliite?+
Where is erniggliite found?+
How much is erniggliite worth?+
Is erniggliite safe to handle?+
What rocks look like erniggliite?+
What minerals are found with erniggliite?+
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Find erniggliite on the map
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