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. Écrinsite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Écrinsite typically shows a metallic luster.
- 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 pale gray-green; luster reads metallic on Écrinsite and vitreous on Tschermakite.
How to tell apart: Actinolite is the harder of the two (Mohs 5.5-6 vs. 3-3.5); streak differs, so Écrinsite leaves black, Actinolite leaves white; luster reads metallic on Écrinsite and vitreous to 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
- Metamorphic Rocks
Where rockhounds find écrinsite
Classic worldwide localities
- Massif des Écrins, France
Field-hunting tip
Look in metamorphic rocks country, the host setting where écrinsite typically forms. If you start seeing epidote, albite, chlorite in float, you are in the right ground. Field specimens usually show a prismatic crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find écrinsite on the map
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