Stoiberite is an extremely rare copper vanadate mineral first discovered in the fumaroles of the Izalco Volcano. Collectors typically find it as microscopic, black tabular crystals forming thin encrustations on volcanic substrates.

Hardness

Mohs

Luster

Metallic

Streak

Reddish Brown

Transparency

Translucent

mineralrare

Stoiberite

Hardness: 3
Luster: Metallic
Streak: Reddish Brown
Transparency: Translucent

Is this stoiberite?

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 stoiberite with a known reference. Stoiberite sits at Mohs 3, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Stoiberite leaves a reddish brown streak.
3
Read the luster
Hold the specimen under a strong light. Stoiberite typically shows a metallic luster.
4
Match the color range
Compare against the expected color range: black.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular to blocky crystals, often as crusts.

Often confused with

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

How to tell apart: Streak differs, so Stoiberite leaves reddish brown, Blossite leaves red-brown.

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Often found alongside stoiberite

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

All properties

Chemical formula: Cu₅V₂O₁₀
Mohs hardness: 3
Density: 5 g/cm³
Colors: Black
Streak: Reddish Brown
Luster: Metallic
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Tabular to Blocky Crystals, Often as Crusts
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Fumarolic Encrustations On Volcanic Rocks

Where rockhounds find stoiberite

Classic worldwide localities

Izalco Volcano, El Salvador

Field-hunting tip

Look in fumarolic encrustations on volcanic rocks country, the host setting where stoiberite typically forms. If you start seeing ziesite, thenardite, sylvite in float, you are in the right ground. Field specimens usually show a tabular to blocky crystals, often as crusts habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify stoiberite?+

Mohs hardness is 3. It typically shows a metallic luster. The streak is reddish brown. Common colors include black.

Where is stoiberite found?+

Notable localities include Izalco Volcano, El Salvador.

Is stoiberite safe to handle?+

It contains toxic constituents. Contains copper and vanadium, which are toxic if ingested or inhaled as dust; wash hands thoroughly after handling. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like stoiberite?+

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

What minerals are found with stoiberite?+

Stoiberite commonly co-occurs with Ziesite, Thenardite, Sylvite, Halite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does stoiberite form in?+

Stoiberite typically forms in fumarolic encrustations on volcanic rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is stoiberite used for?+

Stoiberite is used in collector.

Find stoiberite on the map

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