Guettardite is a rare lead-arsenic sulfosalt primarily found in the famous Binn Valley of Switzerland. It typically forms as small, steel-gray metallic crystals embedded within dolomitic rocks, often requiring magnification for accurate identification due to its similarity to other sulfosalt species.
Is this guettardite?
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 guettardite with a known reference. Guettardite sits at Mohs 4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brownish.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: grayish black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular, anhedral grains.
Often confused with
Guettardite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Guettardite is noticeably harder (Mohs 4 vs. 3); streak differs, so Guettardite leaves brownish, Sartorite leaves chocolate-brown.
How to tell apart: Guettardite is noticeably harder (Mohs 4 vs. 3); streak differs, so Guettardite leaves brownish, Baumhauerite leaves chocolate-brown.
Often found alongside guettardite
Minerals reported to co-occur with guettardite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- PbSbAsS₄
- Mohs hardness
- 4
- Density
- 5.26 g/cm³
- Colors
- Streak
- Brownish
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Acicular, anhedral grains
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- Of low-temperature hydrothermal origin, in marbles (Madoc, Canada; Seravezza, Italy)
Where rockhounds find guettardite
Classic worldwide localities
- Brobdingnag mine, near Silverton, San Juan Co., Colorado, USA
- Madoc, Ontario, Canada (type locality)
- Jas Roux deposit, 10 km east of Chapelle-en-Valgaudemar, Hautes-Alpes, France
- Pitone, Tognetti, and Ceragiola marble quarries, near Seravezza, Tuscany, Italy
- Novoye, Khaydarkan, Fergana Valley, Alai Range, Kyrgyzstan
Field-hunting tip
Where it forms: Of low-temperature hydrothermal origin, in marbles (Madoc, Canada; Seravezza, Italy). If you start seeing pyrite, sphalerite, wurtzite in float, you are in the right ground. Typical habit: acicular, anhedral grains. Train your eye for that shape before scanning the outcrop.
Common questions
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Find guettardite on the map
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