Écrinsite is a rare silver thallium lead sulfosalt, typically dark gray. It occurs in low-temperature hydrothermal origin related to tectonometamorphism. It was first described from Jas Roux sulfosalt deposit, Parc national des Écrins, Hautes-Alpes, France.
Is this écrinsite?
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 écrinsite with a known reference. Écrinsite 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: black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: dark gray.
- 5Look at form & habitCrystal system: triclinic. Typical habit: prismatic crystals.
Often confused with
Écrinsite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Hornblende is the harder of the two (Mohs 5-6 vs. 3-3.5); streak differs, so Écrinsite leaves black, Hornblende leaves grayish-white; luster reads metallic on Écrinsite and vitreous on Hornblende.
How to tell apart: Tschermakite is the harder of the two (Mohs 5-6 vs. 3-3.5); streak differs, so Écrinsite leaves black, Tschermakite leaves greenish white; luster reads metallic on Écrinsite and vitreous on Tschermakite.
How to tell apart: Actinolite is the harder of the two (Mohs 5-6 vs. 3-3.5); streak differs, so Écrinsite leaves black, Actinolite leaves white; luster reads metallic on Écrinsite and vitreous, silky on Actinolite.
Often found alongside écrinsite
Minerals reported to co-occur with écrinsite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- AgTl₃Pb₄As₁₁Sb₉S₃₆
- Mohs hardness
- 3-3.5
- Density
- 4.96 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Triclinic
- Crystal habit
- Prismatic crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Of low-temperature hydrothermal origin related to tectonometamorphism
Where rockhounds find écrinsite
Classic worldwide localities
- Jas Roux sulfosalt deposit, Parc national des Écrins, Hautes-Alpes, France
Field-hunting tip
Where it forms: Of low-temperature hydrothermal origin related to tectonometamorphism. If you start seeing jasrouxite, stibnite, smithite in float, you are in the right ground. Typical habit: prismatic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
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Find écrinsite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
