Cyanochroite is a rare copper-bearing sulfate mineral primarily found in volcanic fumarole environments. It typically forms delicate blue to bluish-green tabular crystals or efflorescences that are highly susceptible to dehydration, requiring careful storage in a dry environment.

Hardness

2-2.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Cyanochroite

Hardness: 2-2.5
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this cyanochroite?

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

Often confused with

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

Often found alongside cyanochroite

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

All properties

Chemical formula: K₂Cu(SO₄)₂·6H₂O
Mohs hardness: 2-2.5
Density: 2.22 g/cm³
Colors: Green blue
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Tabular crystals, crusts, efflorescences
Cleavage: On {201}, perfect
Rarity: Rare
Uses: Collector
Host rock: A rare product of fumarolic action (Vesuvius, Italy)

Where rockhounds find cyanochroite

Classic worldwide localities

Vesuvius, Campania, Italy
Laurium, Greece, in slag

Field-hunting tip

Where it forms: A rare product of fumarolic action (Vesuvius, Italy). If you start seeing thenardite, gypsum, epsomite in float, you are in the right ground. Typical habit: tabular crystals, crusts, efflorescences. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify cyanochroite?+

Mohs hardness is 2-2.5. Luster: vitreous. The streak is white. Common colors include green blue.

Where is cyanochroite found?+

Notable localities include Vesuvius, Campania, Italy; Laurium, Greece, in slag.

Is cyanochroite safe to handle?+

Cyanochroite contains copper. Contains copper; wash hands thoroughly after handling to avoid ingestion or skin irritation. Store in a sealed container to prevent dehydration and dust inhalation.

What rocks look like cyanochroite?+

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

What minerals are found with cyanochroite?+

Cyanochroite commonly co-occurs with Thenardite, Gypsum, Epsomite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does cyanochroite form in?+

Where it forms: A rare product of fumarolic action (Vesuvius, Italy). Working float back to the host body is the standard way to chase a fresh occurrence.

What is cyanochroite used for?+

Cyanochroite is used in collector.

Find cyanochroite on the map

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