Fangite is a rare thallium arsenic sulfosalt typically found as thin crusts or small deep red to maroon aggregates in hydrothermal deposits. It is a highly sought-after species for mineral collectors due to its rarity and association with other thallium-bearing minerals.
Is this fangite?
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 fangite with a known reference. Fangite sits at Mohs 2-2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: orange.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, tarnishing to metallic.
- 4Match the color rangeCompare against the expected color range: deep dark brown, red.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: microcrystalline aggregates, crusts, or radiating crystals.
Often confused with
Fangite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Fangite leaves orange, Orpiment leaves pale lemon-yellow; luster reads vitreous, tarnishing to metallic on Fangite and resinous, pearly on cleavage surface on Orpiment.
How to tell apart: Streak differs, so Fangite leaves orange, Realgar leaves red-orange to red; luster reads vitreous, tarnishing to metallic on Fangite and resinous to greasy on Realgar.
Often found alongside fangite
Minerals reported to co-occur with fangite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Tl₃AsS₄
- Mohs hardness
- 2-2.5
- Density
- 6.185 g/cm³
- Colors
- Deep dark brownRed
- Streak
- Orange
- Luster
- Vitreous, tarnishing to metallic
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Microcrystalline aggregates, crusts, or radiating crystals
- Cleavage
- Indistinct
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a sediment-hosted disseminated gold deposit, in sulfide-rich carbonaceous ore, probably formed by alteration of Tl-As-rich sulfosalts or sulfides
Where rockhounds find fangite
Classic worldwide localities
- Mercur gold deposit, southern Oquirrh Mountains, about 56 km southwest of Salt Lake City, Tooele Co., USA (type locality)
Field-hunting tip
Where it forms: In a sediment-hosted disseminated gold deposit, in sulfide-rich carbonaceous ore, probably formed by alteration of Tl-As-rich sulfosalts or sulfides. If you start seeing pyrite, realgar, orpiment in float, you are in the right ground. Typical habit: microcrystalline aggregates, crusts, or radiating crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify fangite?+
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What rocks look like fangite?+
What minerals are found with fangite?+
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Find fangite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
