Blossite is a rare copper vanadium oxide that forms black equant anhedral crystals. Associated minerals include fingerite, stoiberite and mcbirneyite. It was first described from the summit crater of Izalco volcano, El Salvador.

Hardness

Mohs

Luster

Metallic

Streak

Red-brown

Transparency

Opaque

mineralrare

Blossite

Hardness: 3
Luster: Metallic
Streak: Red-brown
Transparency: Opaque

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Is this blossite?

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 blossite with a known reference. Blossite 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. Streak: red-brown.
3
Read the luster
Hold the specimen under a strong light. Luster: metallic.
4
Match the color range
Compare against the expected color range: black.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: anhedral grains.

Often confused with

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

mineral

Chalcomenite

Mohs 2-2.5

How to tell apart: Streak differs, so Blossite leaves red-brown, Chalcomenite leaves light blue; luster reads metallic on Blossite and vitreous on Chalcomenite.

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Often found alongside blossite

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

All properties

Chemical formula: Cu₂V⁵⁺₂O₇
Mohs hardness: 3
Density: 3.95-3.97 g/cm³
Colors: Black
Streak: Red-brown
Luster: Metallic
Transparency: Opaque
Crystal system: Orthorhombic
Crystal habit: Anhedral grains
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: A very rare sublimate, probably formed between 100–200°C, from the outer sulfate zone of a fumarole in the crater of a basaltic composite volcano

Where rockhounds find blossite

Classic worldwide localities

Summit crater of Izalco Volcano, San Salvador (type locality)

Field-hunting tip

Where it forms: A very rare sublimate, probably formed between 100–200°C, from the outer sulfate zone of a fumarole in the crater of a basaltic composite volcano. If you start seeing fingerite, stoiberite, mcbirneyite in float, you are in the right ground. Typical habit: anhedral grains. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify blossite?+

Mohs hardness is 3. Luster: metallic. The streak is red-brown. Common colors include black.

Where is blossite found?+

Notable localities include Summit crater of Izalco Volcano, San Salvador (type locality).

Is blossite safe to handle?+

Blossite contains copper and vanadium. Contains copper and vanadium, which are toxic if ingested or inhaled as dust. Wash hands thoroughly after handling and avoid creating dust.

What rocks look like blossite?+

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

What minerals are found with blossite?+

Blossite commonly co-occurs with Fingerite, Stoiberite, Mcbirneyite, Ziesite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does blossite form in?+

Where it forms: A very rare sublimate, probably formed between 100–200°C, from the outer sulfate zone of a fumarole in the crater of a basaltic composite volcano. Working float back to the host body is the standard way to chase a fresh occurrence.

What is blossite used for?+

Blossite is used in collector.

Find blossite on the map

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