Kröhnkite is a rare hydrated sodium copper sulfate characterized by its distinct bright azure-blue color and vitreous luster. It forms primarily as a secondary mineral in the arid oxidation zones of copper deposits, often found as tabular crystals or fibrous crusts associated with other copper sulfates.

Hardness

2.5-3

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineraluncommon

Kröhnkite

Hardness: 2.5-3
Luster: Vitreous
Streak: White
Transparency: Translucent

Is this kröhnkite?

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 kröhnkite with a known reference. Kröhnkite sits at Mohs 2.5-3 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Kröhnkite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Kröhnkite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: blue, blue-green.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals, fibrous, crusts, massive.

Often confused with

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

How to tell apart: Streak differs — Kröhnkite leaves white, Brochantite leaves pale-green.

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Often found alongside kröhnkite

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

All properties

Chemical formula: Na₂Cu(SO₄)₂·2H₂O
Mohs hardness: 2.5-3
Density: 2.36 g/cm³
Colors: Blue Blue-green
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Tabular Crystals, Fibrous, Crusts, Massive
Cleavage: Perfect On {010}, Good On {110}
Rarity: Uncommon
Uses: Collector
Host rock: Arid Oxidation Zones of Copper Sulfide Deposits
Typical price: $15-100 per specimen depending on crystal quality

Where rockhounds find kröhnkite

Classic worldwide localities

Chuquicamata Mine, Chile
Calama, Chile
Alcaparrosa Mine, Chile
Copiapo, Chile

Field-hunting tip

Look in arid oxidation zones of copper sulfide deposits country — that is the host setting where kröhnkite typically forms. If you start seeing chalcanthite, brochantite, atacamite in float, you are in the right ground. Field specimens usually show a tabular crystals, fibrous, crusts, massive habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify kröhnkite?+

Mohs hardness is 2.5-3. It typically shows a vitreous luster. The streak is white. Common colors include blue, blue-green.

Where is kröhnkite found?+

Notable localities include Chuquicamata Mine, Chile; Calama, Chile; Alcaparrosa Mine, Chile; Copiapo, Chile.

How much is kröhnkite worth?+

Typical asking prices fall in the range of $15-100 per specimen depending on crystal quality. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like kröhnkite?+

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

What minerals are found with kröhnkite?+

Kröhnkite commonly co-occurs with Chalcanthite, Brochantite, Atacamite, Gypsum, Copiapite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does kröhnkite form in?+

Kröhnkite typically forms in arid oxidation zones of copper sulfide deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is kröhnkite used for?+

Kröhnkite is used in collector.

Find kröhnkite on the map

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