Fornacite is a rare lead copper chromate-arsenate mineral typically found in the oxidation zones of ore deposits. It is best identified by its distinct yellowish-green color and bladed, tabular habit, often occurring alongside closely related vauquelinite.
Is this fornacite?
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 fornacite with a known reference. Fornacite sits at Mohs 3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: saffron-yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: yellow, green, olive green, greenish yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: aggregates.
Often confused with
Fornacite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Fornacite leaves saffron-yellow, Vauquelinite leaves greenish to brownish; luster reads vitreous on Fornacite and adamantine to resinous on Vauquelinite.
How to tell apart: Streak differs, so Fornacite leaves saffron-yellow, Mimetite leaves white; luster reads vitreous on Fornacite and resinous to subadamantine on Mimetite.
Often found alongside fornacite
Minerals reported to co-occur with fornacite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Pb₂Cu(CrO₄)(AsO₄)(OH)
- Mohs hardness
- 3
- Density
- 6.27 g/cm³
- Streak
- Saffron-yellow
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Aggregates
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare mineral in the oxidized zones of some hydrothermal base-metal deposits
Where rockhounds find fornacite
Classic worldwide localities
- Blue Bell mine, near Baker, San Bernardino Co., California, USA
- Socorro Peak, Socorro Co., New Mexico, USA
- Killie mine, Spruce Mountain district, Elko Co., and in the Silver Coin mine, near Valmy, Iron Point district, Humboldt Co., Nevada, USA
- Djoué and Renéville, Congo Republic
- Argent Pb–Zn mines, about 100 km east of Johannesburg, Transvaal, South Africa
- Seh Changi mine, near Neybaud, Khorassan, and at Sebarz, Iran
Field-hunting tip
Where it forms: A rare mineral in the oxidized zones of some hydrothermal base-metal deposits. If you start seeing dioptase, wulfenite, hemihedrite in float, you are in the right ground. Typical habit: aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify fornacite?+
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Is fornacite safe to handle?+
What rocks look like fornacite?+
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Find fornacite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
