Lyonsite is a rare copper-iron vanadate mineral typically found as small, black tabular crystals or crusts. It was discovered in the high-temperature fumarole vents of the Izalco Volcano, where it forms through volcanic gas sublimation.
Is this lyonsite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry 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.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: dark gray.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: euhedral crystals, lath.
Often confused with
Lyonsite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Lyonsite leaves dark gray, Thénardite leaves white; luster reads metallic on Lyonsite and vitreous to resinous on Thénardite.
How to tell apart: Streak differs, so Lyonsite leaves dark gray, Vanadinite leaves white to pale red or pale yellow; luster reads metallic on Lyonsite and subresinous to subadamantine on Vanadinite.
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
- 4.215 g/cm³
- Colors
- Streak
- Dark gray
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Euhedral crystals, lath
- Cleavage
- Good on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In summit crater fumaroles, as a sublimate formed at ≤800°C
Where rockhounds find lyonsite
Classic worldwide localities
- Izalco volcano, El Salvador
Field-hunting tip
Where it forms: In summit crater fumaroles, as a sublimate formed at ≤800°C. If you start seeing thenardite, howardevansite in float, you are in the right ground. Typical habit: euhedral crystals, lath. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify lyonsite?+
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Find lyonsite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
