Philrothite is a very rare thallium-arsenic sulfosalt primarily found in the famous Binn Valley localities of Switzerland. It typically appears as small lead-gray tabular crystals embedded within dolomitic marble and is highly sought after by advanced mineral collectors due to its restricted occurrence.
Is this philrothite?
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 philrothite with a known reference. Philrothite 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: dark brown.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, massive.
Often confused with
Philrothite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Philrothite leaves dark brown, Sartorite leaves chocolate-brown.
How to tell apart: Philrothite is noticeably harder (Mohs 3-3.5 vs. 1.5-2); streak differs, so Philrothite leaves dark brown, Hutchinsonite leaves red; luster reads metallic on Philrothite and adamantine to submetallic on Hutchinsonite.
How to tell apart: Streak differs, so Philrothite leaves dark brown, Gratonite leaves black.
Often found alongside philrothite
Minerals reported to co-occur with philrothite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- TlAs₃S₅
- Mohs hardness
- 3-3.5
- Density
- 4.635 g/cm³
- Colors
- Streak
- Dark brown
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals, massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A product of late-stage Tl- and As-bearing hydrothermal solutions during alpine metamorphism
Where rockhounds find philrothite
Classic worldwide localities
- Lengenbach quarry, Binn Valley, Valais, Switzerland
Field-hunting tip
Where it forms: A product of late-stage Tl- and As-bearing hydrothermal solutions during alpine metamorphism. If you start seeing realgar, smithite, rutile in float, you are in the right ground. Typical habit: tabular crystals, massive. Train your eye for that shape before scanning the outcrop.
Common questions
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Find philrothite on the map
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