Molybdofornacite is a rare secondary mineral found in the oxidation zones of lead-bearing ore deposits. It typically appears as bright yellow to greenish-yellow tabular crystals or thin crusts, often associated with other rare arsenates and chromates at world-class localities like Tsumeb.
Is this molybdofornacite?
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 molybdofornacite with a known reference. Molybdofornacite sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: adamantine.
- 4Match the color rangeCompare against the expected color range: light green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: lath, pistolitic.
Often confused with
Molybdofornacite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Molybdofornacite leaves pale yellow, Fornacite leaves saffron-yellow; luster reads adamantine on Molybdofornacite and vitreous on Fornacite.
How to tell apart: Streak differs, so Molybdofornacite leaves pale yellow, Vauquelinite leaves greenish to brownish.
Often found alongside molybdofornacite
Minerals reported to co-occur with molybdofornacite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CuPb₂MoO₄AsO₄(OH)
- Mohs hardness
- 3-4
- Density
- 6.6 g/cm³
- Colors
- Streak
- Pale yellow
- Luster
- Adamantine
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Lath, pistolitic
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In the deep oxidation zone of a dolostone-hosted hydrothermal polymetallic ore deposit (Tsumeb, Namibia)
Where rockhounds find molybdofornacite
Classic worldwide localities
- Tonopah-Belmont mine, Big Horn Mountains, Osborne district, Maricopa Co., and the Rawhide mine, Buckskin Mountains, Mohave Co., Arizona, USA
- Bullfrog #2 claim, near Silver Hill, three km northwest of Magdalena, Socorro Co., and in the Tres Hermanas Mountains, Mahoney district, Luna Co., New Mexico, USA
- Silver Coin mine, near Valmy, Iron Point district, Humboldt Co., Nevada, USA
- Tsumeb, Namibia
- La Cobradita, Sonora, Mexico
Field-hunting tip
Where it forms: In the deep oxidation zone of a dolostone-hosted hydrothermal polymetallic ore deposit (Tsumeb, Namibia). If you start seeing dioptase, duftite, wulfenite in float, you are in the right ground. Typical habit: lath, pistolitic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify molybdofornacite?+
Where is molybdofornacite found?+
Is molybdofornacite safe to handle?+
What rocks look like molybdofornacite?+
What minerals are found with molybdofornacite?+
What kind of rock does molybdofornacite form in?+
What is molybdofornacite used for?+
Find molybdofornacite on the map
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