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.

Hardness

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrareSulfosalt family

Philrothite

Hardness: 3
Luster: Metallic
Streak: Black
Transparency: Opaque

No image

Is this philrothite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch philrothite with a known reference. Philrothite sits at Mohs 3, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Philrothite leaves a black streak.
3
Read the luster
Hold the specimen under a strong light. Philrothite typically shows a metallic luster.
4
Match the color range
Compare against the expected color range: lead-gray, black.
5
Look at form & habit
Crystal 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.

mineral

Sartorite

Mohs 3

How to tell apart: Streak differs, so Philrothite leaves black, Sartorite leaves chocolate-brown.

How to tell apart: Philrothite is noticeably harder (Mohs 3 vs. 1.5-2); streak differs, so Philrothite leaves black, Hutchinsonite leaves red; luster reads metallic on Philrothite and adamantine on Hutchinsonite.

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
Density: 5.32 g/cm³
Colors: Lead-gray Black
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Monoclinic
Crystal habit: Tabular Crystals, Massive
Cleavage: Good
Rarity: Rare
Uses: Collector
Host rock: Dolomitic Marble
Typical price: $200-2000+ for rare specimens

Where rockhounds find philrothite

Classic worldwide localities

Lengenbach Quarry, Binn Valley, Switzerland

Field-hunting tip

Look in dolomitic marble country, the host setting where philrothite typically forms. If you start seeing sartorite, realgar, pyrite in float, you are in the right ground. Field specimens usually show a tabular crystals, massive habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify philrothite?+

Mohs hardness is 3. It typically shows a metallic luster. The streak is black. Common colors include lead-gray, black.

Where is philrothite found?+

Notable localities include Lengenbach Quarry, Binn Valley, Switzerland.

How much is philrothite worth?+

Typical asking prices fall in the range of $200-2000+ for rare specimens. Quality, size, and provenance can move individual specimens well outside that range.

Is philrothite safe to handle?+

It contains toxic constituents. Contains thallium and arsenic; handle with gloves and wash hands thoroughly after contact. Do not inhale dust. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like philrothite?+

Philrothite is most often confused with Sartorite, Hutchinsonite, Gratonite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with philrothite?+

Philrothite commonly co-occurs with Sartorite, Realgar, Pyrite, Dolomite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does philrothite form in?+

Philrothite typically forms in dolomitic marble. Working float back to the host body is the standard way to chase a fresh occurrence.

What is philrothite used for?+

Philrothite is used in collector.

Find philrothite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.