Fettelite is an extremely rare silver-arsenic sulfosalt often found in association with other silver minerals in hydrothermal deposits. Collectors should look for its distinctive dark red to black metallic appearance and perfect basal cleavage in small, tabular specimens.
Is this fettelite?
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 fettelite with a known reference. Fettelite sits at Mohs 3.75, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: dark vermillion.
- 3Read the lusterHold the specimen under a strong light. Luster: submetallic to metallic to adamantine.
- 4Match the color rangeCompare against the expected color range: dark violet, scarlet red.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: flakes, hexagonal, micaceous.
Often confused with
Fettelite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Fettelite is noticeably harder (Mohs 3.75 vs. 2-2.5); streak differs, so Fettelite leaves dark vermillion, Proustite leaves vermilion; luster reads submetallic to metallic to adamantine on Fettelite and adamantine on Proustite.
How to tell apart: Fettelite is noticeably harder (Mohs 3.75 vs. 2.5); streak differs, so Fettelite leaves dark vermillion, Pyrargyrite leaves purplish red; luster reads submetallic to metallic to adamantine on Fettelite and adamantine on Pyrargyrite.
Often found alongside fettelite
Minerals reported to co-occur with fettelite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ag₁₆HgAs₄S₁₅
- Mohs hardness
- 3.75
- Density
- 6.29 g/cm³
- Colors
- Dark violetScarlet red
- Streak
- Dark vermillion
- Luster
- Submetallic to metallic to adamantine
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Flakes, hexagonal, micaceous
- Cleavage
- Perfect on {0001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare mineral in low-temperature hydrothermal, silver-sulfosalt veins
Where rockhounds find fettelite
Classic worldwide localities
- Glasberg quarry, Nieder-Beerbach, 10 km south of Darmstadt, Odenwald, Hesse, Germany (type locality)
- Chañarcillo, Copiapó Province, Chile
Field-hunting tip
Where it forms: A rare mineral in low-temperature hydrothermal, silver-sulfosalt veins. If you start seeing proustite, pearceite, xanthoconite in float, you are in the right ground. Typical habit: flakes, hexagonal, micaceous. Train your eye for that shape before scanning the outcrop.
Common questions
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Find fettelite on the map
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