Fassinaite is an extremely rare lead thiosulfate mineral that typically occurs as small, tabular crystals. It is primarily found as an alteration product of galena in lead-rich oxidation zones. Due to its rarity and delicate nature, it is highly sought after by advanced systematic mineral collectors.
Is this fassinaite?
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 fassinaite with a known reference. Fassinaite sits at Mohs 1.5-2, 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 to adamantine.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals.
Often confused with
Fassinaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads vitreous to adamantine on Fassinaite and adamantine, resinous to vitreous on Anglesite.
How to tell apart: Cerussite is the harder of the two (Mohs 3-3.5 vs. 1.5-2); luster reads vitreous to adamantine on Fassinaite and adamantine, tending toward vitreous, resinous on Cerussite.
Often found alongside fassinaite
Minerals reported to co-occur with fassinaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb₂(CO₃)(SO₃S)
- Mohs hardness
- 1.5-2
- Density
- 6.084 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous to adamantine
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral in the weathering zone of a polymetallic hydrothermal deposit
Where rockhounds find fassinaite
Classic worldwide localities
- Fassina quarry, Italy
- Laurion, Greece
Field-hunting tip
Where it forms: A secondary mineral in the weathering zone of a polymetallic hydrothermal deposit. If you start seeing galena, quartz, anglesite in float, you are in the right ground. Typical habit: tabular crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify fassinaite?+
Where is fassinaite found?+
Is fassinaite safe to handle?+
What rocks look like fassinaite?+
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Find fassinaite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
