Olsacherite is an exceptionally rare lead sulfate-selenate mineral discovered in the selenium-rich hydrothermal deposits of Argentina. Collectors should look for small, transparent to translucent crystals often associated with other rare selenium minerals in secondary oxidation zones.
Is this olsacherite?
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 olsacherite with a known reference. Olsacherite 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: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, dull if coated.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular.
Often confused with
Olsacherite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside olsacherite
Minerals reported to co-occur with olsacherite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb₂(SeO₄)(SO₄)
- Mohs hardness
- 3-3.5
- Density
- 6.55 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous, dull if coated
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular
- Cleavage
- Good on {101}; fair on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral in the oxidized zone of selenium-bearing hydrothermal mineral deposits
Where rockhounds find olsacherite
Classic worldwide localities
- Pacajake mine, Hiaco, 24 km east-northeast of Colquechaca, and in the El Dragón mine, 30 km southwest of Cerro Rico de Potosí, Potosí, Bolivia
- Cerro de Cacheuta, Mendoza Province, Argentina
- Baccu Locci mine, near Villaputzu, Sarrabus district, Sardinia, Italy
Field-hunting tip
Where it forms: A rare secondary mineral in the oxidized zone of selenium-bearing hydrothermal mineral deposits. If you start seeing penroseite, chalcomenite, ahlfeldite in float, you are in the right ground. Typical habit: acicular. Train your eye for that shape before scanning the outcrop.
Common questions
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Find olsacherite on the map
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