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, so 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, 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.