Lyonsite is a rare copper-iron vanadate mineral typically found as small, bright yellow tabular crystals or crusts. It was discovered in the high-temperature fumarole vents of the Izalco Volcano, where it forms through volcanic gas sublimation.

Hardness

3-3.5

Mohs

Luster

Vitreous

Streak

Yellow

Transparency

Translucent

mineralrare

Lyonsite

Hardness: 3-3.5
Luster: Vitreous
Streak: Yellow
Transparency: Translucent

Is this lyonsite?

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 lyonsite with a known reference. Lyonsite sits at Mohs 3-3.5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Lyonsite leaves a yellow streak.
3
Read the luster
Hold the specimen under a strong light. Lyonsite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: yellow, brownish-yellow.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: tabular crystals, incrustations.

Often confused with

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

mineral

Thenardite

Mohs 2.5-3

How to tell apart: Streak differs — Lyonsite leaves yellow, Thenardite leaves white.

How to tell apart: Streak differs — Lyonsite leaves yellow, Vanadinite leaves white; luster reads vitreous on Lyonsite and resinous on Vanadinite.

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Often found alongside lyonsite

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

All properties

Chemical formula: Cu₃Fe₄(VO₄)₆
Mohs hardness: 3-3.5
Density: 3.55 g/cm³
Colors: Yellow Brownish-yellow
Streak: Yellow
Luster: Vitreous
Transparency: Translucent
Crystal system: Orthorhombic
Crystal habit: Tabular Crystals, Incrustations
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Fumarole Deposits
Typical price: $50-300 per specimen

Where rockhounds find lyonsite

Classic worldwide localities

Izalco Volcano, El Salvador

Field-hunting tip

Look in fumarole deposits country — that is the host setting where lyonsite typically forms. If you start seeing thenardite, vanadinite, hematite in float, you are in the right ground. Field specimens usually show a tabular crystals, incrustations habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify lyonsite?+

Mohs hardness is 3-3.5. It typically shows a vitreous luster. The streak is yellow. Common colors include yellow, brownish-yellow.

Where is lyonsite found?+

Notable localities include Izalco Volcano, El Salvador.

How much is lyonsite worth?+

Typical asking prices fall in the range of $50-300 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

Is lyonsite safe to handle?+

It contains toxic constituents. Contains copper and vanadium. Handle with care, avoid inhalation of dust, and wash hands thoroughly after handling. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like lyonsite?+

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

What minerals are found with lyonsite?+

Lyonsite commonly co-occurs with Thenardite, Vanadinite, Hematite, Sylvite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does lyonsite form in?+

Lyonsite typically forms in fumarole deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is lyonsite used for?+

Lyonsite is used in collector.

Find lyonsite on the map

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