Coiraite is an exceptionally rare sulfosalt mineral primarily found in the tin-rich polymetallic deposits of Bolivia. It typically occurs as small, dark, tabular to platy crystals that are structurally related to the cylindrite group, often requiring analytical techniques for positive field identification.

Hardness

Mohs

Luster

Metallic to dull

Streak

Dark gray to almost black

Transparency

Opaque

mineralrareCylindrite Group family

Coiraite

Hardness: ~2
Luster: Metallic to dull
Streak: Dark gray to almost black
Transparency: Opaque

Is this coiraite?

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 coiraite with a known reference. Coiraite sits at Mohs ~2, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: dark gray to almost black.
3
Read the luster
Hold the specimen under a strong light. Luster: metallic to dull.
4
Match the color range
Compare against the expected color range: gray.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: colloform, massive.

Often confused with

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

mineral

Cylindrite

Mohs 2.5

How to tell apart: Streak differs, so Coiraite leaves dark gray to almost black, Cylindrite leaves black.

How to tell apart: Streak differs, so Coiraite leaves dark gray to almost black, Franckeite leaves grayish black.

Compare →

Often found alongside coiraite

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

All properties

Chemical formula: (Pb,Sn)₁₂.₅As₃FeSn₅S₂₈
Mohs hardness: ~2
Density: 5.92 g/cm³
Colors: Gray
Streak: Dark gray to almost black
Luster: Metallic to dull
Transparency: Opaque
Crystal system: Monoclinic
Crystal habit: Colloform, massive
Cleavage: Perfect on (001)
Rarity: Rare
Uses: Collector
Host rock: A primary mineral in a telescoped Ag-Sn-Zn polymetallic hydrothermal vein deposit

Where rockhounds find coiraite

Classic worldwide localities

Pirquitas deposit, Jujuy Province, northwest Argentina

Field-hunting tip

Where it forms: A primary mineral in a telescoped Ag-Sn-Zn polymetallic hydrothermal vein deposit. If you start seeing franckeite, cylindrite, pyrite-marcasite in float, you are in the right ground. Typical habit: colloform, massive. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify coiraite?+

Mohs hardness is ~2. Luster: metallic to dull. The streak is dark gray to almost black. Common colors include gray.

Where is coiraite found?+

Notable localities include Pirquitas deposit, Jujuy Province, northwest Argentina.

Is coiraite safe to handle?+

Coiraite contains arsenic and lead and calls for real care. Contains lead and antimony; wash hands thoroughly after handling and avoid inhaling dust.

What rocks look like coiraite?+

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

What minerals are found with coiraite?+

Coiraite commonly co-occurs with Franckeite, Cylindrite, Pyrite-marcasite, Hocartite, Ag-rich rhodostannite, Arsenopyrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does coiraite form in?+

Where it forms: A primary mineral in a telescoped Ag-Sn-Zn polymetallic hydrothermal vein deposit. Working float back to the host body is the standard way to chase a fresh occurrence.

What is coiraite used for?+

Coiraite is used in collector.

Find coiraite on the map

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