Koutekite is a rare copper-arsenic mineral that typically forms as anhedral masses within hydrothermal vein deposits. It is known for its metallic luster and distinctive silver-white color, which may quickly tarnish to a duller hue upon exposure to air.

Hardness

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrare

Koutekite

Hardness: ~4
Luster: Metallic
Streak: Black
Transparency: Opaque

Is this koutekite?

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 koutekite with a known reference. Koutekite sits at Mohs ~4, 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: gray blue.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: microscopic crystals.

Often confused with

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

How to tell apart: Streak differs, so Koutekite leaves black, Algodonite leaves white; luster reads metallic on Koutekite and bright metallic on Algodonite.

How to tell apart: Streak differs, so Koutekite leaves black, Arsenic leaves tin-white; luster reads metallic on Koutekite and nearly metallic on Arsenic.

Compare →

Often found alongside koutekite

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

All properties

Chemical formula: Cu₅As₂
Mohs hardness: ~4
Density: 8.48 g/cm³
Colors: Gray blue
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Hexagonal
Crystal habit: Microscopic crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: In arsenical copper deposits

Where rockhounds find koutekite

Classic worldwide localities

Mohawk, Keeweenaw Co., Michigan, USA
Černý Důl mine, Krkonoše (Giant Mountains), Czech Republic (type locality)
Daluis, Alpes-Maritimes, France
Lautaret, Hautes-Alpes, France
Wasserfall, about 20 km northwest of Belfort, Haute-Saône, France
Långban, and at the Harstigen mine, near Persberg, Värmland, Sweden

Field-hunting tip

Where it forms: In arsenical copper deposits. If you start seeing paxite, arsenic, silver in float, you are in the right ground. Typical habit: microscopic crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify koutekite?+

Mohs hardness is ~4. Luster: metallic. The streak is black. Common colors include gray blue.

Where is koutekite found?+

Notable localities include Mohawk, Keeweenaw Co., Michigan, USA; Černý Důl mine, Krkonoše (Giant Mountains), Czech Republic (type locality); Daluis, Alpes-Maritimes, France; Lautaret, Hautes-Alpes, France; Wasserfall, about 20 km northwest of Belfort, Haute-Saône, France.

Is koutekite safe to handle?+

Koutekite contains arsenic and copper and calls for real care. Contains arsenic, which is toxic; handle with care and wash hands thoroughly after contact to avoid ingestion or inhalation of dust.

What rocks look like koutekite?+

Koutekite is most often confused with Domeykite, Algodonite, Arsenic. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with koutekite?+

Koutekite commonly co-occurs with Paxite, Arsenic, Silver, Skutterudite, Nickeline, Löllingite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does koutekite form in?+

Where it forms: In arsenical copper deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is koutekite used for?+

Koutekite is used in collector.

Find koutekite on the map

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