Lafossaite is a rare thallium halide, typically gray-brown. It is a by sublimation from fumarolic gas. Associated minerals include cannizzarite, galenobismutite and pyrite. It was first described from La Fossa Crater, Vulcano, Aeolian archipelago, Sicily, Italy.
Is this lafossaite?
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 lafossaite with a known reference. Lafossaite sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Lafossaite leaves a off-white to cream streak.
- 3Read the lusterHold the specimen under a strong light. Lafossaite typically shows a resinous to greasy luster.
- 4Match the color rangeCompare against the expected color range: gray-brown.
- 5Look at form & habitCrystal system: cubic. Typical habit: subhedral to euhedral crystals.
Often confused with
Lafossaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Lafossaite leaves off-white to cream, Halite leaves white; luster reads resinous to greasy on Lafossaite and vitreous on Halite.
How to tell apart: Lafossaite is noticeably harder (Mohs 3-4 vs. 2); streak differs, so Lafossaite leaves off-white to cream, Sylvite leaves white; luster reads resinous to greasy on Lafossaite and vitreous on Sylvite.
Often found alongside lafossaite
Minerals reported to co-occur with lafossaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- TlCl
- Mohs hardness
- 3-4
- Density
- 7.212 g/cm³
- Colors
- Streak
- Off-white to Cream
- Luster
- Resinous to Greasy
- Transparency
- Translucent
- Crystal system
- Cubic
- Crystal habit
- Subhedral to Euhedral Crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Volcanic Fumaroles
Where rockhounds find lafossaite
Classic worldwide localities
- La Fossa crater, Vulcano, Aeolian Islands, Italy
Field-hunting tip
Look in volcanic fumaroles country, the host setting where lafossaite typically forms. If you start seeing sal ammoniac, anglesite, galena in float, you are in the right ground. Field specimens usually show a subhedral to euhedral crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find lafossaite on the map
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