Larosite is a rare sulfosalt mineral primarily identified through microanalysis in hydrothermal ore deposits. It typically occurs as tiny, metallic grains embedded within other sulfide minerals, making it a challenging but rewarding find for systematic mineral collectors.

Hardness

3-3.5

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrare

Larosite

Hardness: 3-3.5
Luster: Metallic
Streak: Black
Transparency: Opaque

Is this larosite?

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 larosite with a known reference. Larosite sits at Mohs 3-3.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: black.
3
Read the luster
Hold the specimen under a strong light. Luster: metallic.
4
Match the color range
Compare against the expected color range: black.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: acicular, microscopic crystals.

Often confused with

Larosite vs. its common look-alikes, and how to tell them apart in the field.

mineral

Tennantite

Mohs 3-4.5

How to tell apart: Streak differs, so Larosite leaves black, Tennantite leaves reddish gray.

Often found alongside larosite

Minerals reported to co-occur with larosite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: (Cu,Ag)₂₁PbBiS₁₃
Mohs hardness: 3-3.5
Density: 6.19 g/cm³
Colors: Black
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Orthorhombic
Crystal habit: Acicular, microscopic crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: In the central portion of a layered hydrothermal vein

Where rockhounds find larosite

Classic worldwide localities

Foster mine, Cobalt, Ontario, Canada (type locality)

Field-hunting tip

Where it forms: In the central portion of a layered hydrothermal vein. If you start seeing chalcocite, stromeyerite, arsenopyrite in float, you are in the right ground. Typical habit: acicular, microscopic crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify larosite?+

Mohs hardness is 3-3.5. Luster: metallic. The streak is black. Common colors include black.

Where is larosite found?+

Notable localities include Foster mine, Cobalt, Ontario, Canada (type locality).

Is larosite safe to handle?+

Larosite contains copper and lead. Contains copper, lead, and arsenic; avoid inhalation of dust, handle with care and wash hands thoroughly after handling.

What rocks look like larosite?+

Larosite is most often confused with Tennantite, Tetrahedrite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with larosite?+

Larosite commonly co-occurs with Chalcocite, Stromeyerite, Arsenopyrite, Galena, Tetrahedrite, Polybasite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does larosite form in?+

Where it forms: In the central portion of a layered hydrothermal vein. Working float back to the host body is the standard way to chase a fresh occurrence.

What is larosite used for?+

Larosite is used in collector.

Find larosite on the map

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