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Wulfenite is a lead molybdate mineral with the chemical formula PbMoO4. It is renowned for its vibrant colors, most commonly orange, yellow, and red, and its distinctive tabular or pyramidal crystal habits. It typically forms thin, square, or octagonal tabular crystals, often with bevelled edges, though pyramidal and bipyramidal forms are also observed. Its high luster, ranging from adamantine to resinous, contributes to its visual appeal. Wulfenite is relatively soft and brittle, making it a delicate mineral. It is a secondary mineral found in the oxidized zones of lead deposits.
How to Identify
- Color
- Typically bright orange, yellow, or red; less commonly brown, gray, green, or colorless. The color is often vivid and translucent.
- Luster
- Adamantine to resinous, giving it a brilliant, almost greasy appearance.
- Texture
- Smooth, often with distinct crystal faces. Crystals are typically tabular, sometimes pyramidal.
- Crystal Form
- Most commonly thin, square, or octagonal tabular crystals. Also found as pyramidal, bipyramidal, or granular masses. Crystals can be very sharp and well-formed.
- Cleavage
- Distinct on {011}, but often difficult to observe due to its brittleness and thin crystal habit. Fracture is conchoidal to uneven.
- Geological Environment
- Oxidized zones of lead-zinc-molybdenum hydrothermal ore deposits, often associated with minerals like cerussite, anglesite, mimetite, vanadinite, and limonite. It forms in arid or semi-arid environments where oxidation is prevalent.
Key Facts
- Hardness: 2.5 - 3 on the Mohs scale
- Specific Gravity: 6.5 - 7.0 (very dense due to lead content)
- Crystal System: Tetragonal
- Color: Orange, yellow, red, brown, gray, green, colorless
- Luster: Adamantine to resinous
- Transparency: Transparent to translucent
- Fracture: Conchoidal to uneven
- Cleavage: Distinct on {011}, but often imperfect or difficult to observe
- Composition: Lead molybdate (PbMoO4)
Quick Check
- Color: Bright orange, yellow, red (most common); also brown, gray, green, colorless.
- Luster: Adamantine to resinous.
- Streak: White.
Physical Characteristics
- Crystal Habit: Typically thin, square, or octagonal tabular crystals; also pyramidal, bipyramidal, granular, or massive.
- Cleavage Type: Distinct on {011}, but often imperfect.
- Fracture Type: Conchoidal to uneven.
- Tenacity: Brittle.
- Luster Type: Adamantine to resinous.
Formation
Wulfenite is a secondary mineral that forms in the oxidized zone (supergene zone) of lead-zinc-molybdenum hydrothermal ore deposits. It precipitates from circulating groundwater that has reacted with primary lead sulfides (like galena, PbS) and molybdenum-bearing minerals (like molybdenite, MoS2), often in the presence of oxygen and carbonate or sulfate ions. The molybdenum is typically derived from the oxidation of primary molybdenite or other molybdenum-bearing minerals in the host rock or adjacent intrusions. The lead comes from the oxidation of galena. The presence of vanadium can lead to vanadian wulfenite, and chromium can also substitute, leading to color variations.
Usage
Wulfenite is primarily a collector's mineral due to its striking colors and crystal forms. It is also a minor ore of molybdenum in some localities, though not economically significant on a large scale. Historically, it was a source of lead. Its aesthetic appeal makes it highly sought after for mineral collections and sometimes for lapidary purposes, though its softness makes it challenging to facet.
Age Distribution
Wulfenite forms in the oxidized zones of lead-bearing hydrothermal ore deposits, which can be found in rocks of various geological ages, typically post-ore formation.
Where to Find
Red Cloud Mine, La Paz County, Arizona, USA
Famous for producing some of the world's finest deep orange-red tabular wulfenite crystals, often on a matrix of contrasting minerals.
Los Lamentos, Chihuahua, Mexico
Known for producing large, thick, and often gemmy orange to yellow wulfenite crystals, sometimes with complex forms.
Tsumeb Mine, Oshikoto Region, Namibia
A classic locality for a wide variety of minerals, including wulfenite, which occurs in various colors and habits, often associated with other rare secondary minerals.
Mezica, Slovenia
The type locality for wulfenite, where it was first described. Produces yellow to orange crystals.
Drahanovice, Moravia, Czech Republic
Known for yellow to orange wulfenite crystals.
Bleiberg, Carinthia, Austria
Historically significant locality for wulfenite, producing yellow crystals.
Finding Tips
Target Oxidized Zones
Focus your search on the oxidized (supergene) zones of known lead-zinc-molybdenum deposits. These zones are typically near the surface where groundwater and oxygen have interacted with primary sulfide ores.
Look for Associated Minerals
Wulfenite is often found with other secondary lead minerals such as cerussite (PbCO3), anglesite (PbSO4), mimetite (Pb5(AsO4)3Cl), and vanadinite (Pb5(VO4)3Cl), as well as iron oxides like limonite. The presence of these minerals can indicate a favorable environment for wulfenite.
Examine Vugs and Fractures
Wulfenite crystals typically grow in open spaces, vugs, and fractures within the host rock, where solutions can circulate and precipitate minerals. Look for these cavities.
Identify by Color and Luster
The distinctive bright orange, yellow, or red colors combined with its adamantine to resinous luster are key visual identifiers. Its thin, tabular crystal habit is also very characteristic.
Handle with Care
Wulfenite is soft (Mohs 2.5-3) and brittle. When collecting, use appropriate tools to carefully extract specimens and protect them from damage during transport. Wrap specimens individually in soft material.
Safety Precautions
Wulfenite contains lead, which is a toxic heavy metal. Always wash hands thoroughly after handling specimens. Avoid inhaling dust if breaking or cleaning specimens. Do not ingest. Keep specimens out of reach of children and pets. While the lead is not readily bioavailable from intact crystals, prolonged skin contact or ingestion of dust should be avoided.
Similar Rocks
Crocoite
PbCrO4
Also known as: Red Lead Ore
Vanadinite
Pb5(VO4)3Cl
Also known as: Vanadium Lead Ore
Pyromorphite
Pb5(PO4)3Cl
Also known as: Green Lead Ore
Orpiment
As2S3
Also known as: King's Gold
Scientific Classification
- Mineral Class
- Molybdates (part of the chromate/molybdate/tungstate group)
- Group
- Scheelite Group (isostructural with scheelite, CaWO4)
- Crystal System
- Tetragonal
- Chemical Formula
- PbMoO4
- Composition
- Lead (Pb) 56.43%, Molybdenum (Mo) 18.02%, Oxygen (O) 25.55% (by weight)
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