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. Lyonsite leaves a dark gray streak.
- 3Read the lusterHold the specimen under a strong light. Lyonsite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal 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.
How to tell apart: Streak differs, so Lyonsite leaves dark gray, Thénardite leaves white; luster reads metallic on Lyonsite and vitreous on Thénardite.
How to tell apart: Streak differs, so Lyonsite leaves dark gray, Vanadinite leaves white; luster reads metallic on Lyonsite and 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
- 4.21 g/cm³
- Colors
- Streak
- Dark Gray
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular Crystals, Incrustations
- Cleavage
- Good On {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Fumarole Deposits
Where rockhounds find lyonsite
Classic worldwide localities
- Izalco Volcano, El Salvador
Field-hunting tip
Look in fumarole deposits country, 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
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Find lyonsite on the map
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