Powellite is a molybdenum-bearing member of the scheelite group, most easily recognized by its vibrant yellow fluorescence under short-wave ultraviolet light. Collectors look for its characteristic tetragonal bipyramidal crystals, which are typically found as pseudomorphs after molybdenite or as vug linings in basaltic rocks.
Is this powellite?
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 powellite with a known reference. Powellite sits at Mohs 3.5-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: light yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: subadamantine, resinous, pearly.
- 4Match the color rangeCompare against the expected color range: blue, brown, green yellow, greenish blue, gray.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: crystalline, granular.
Often confused with
Powellite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Powellite leaves light yellow, Scheelite leaves white; luster reads subadamantine, resinous, pearly on Powellite and vitreous to adamantine on Scheelite.
How to tell apart: Streak differs, so Powellite leaves light yellow, Wulfenite leaves white; luster reads subadamantine, resinous, pearly on Powellite and resinous, subadamantine to adamantine on Wulfenite.
Often found alongside powellite
Minerals reported to co-occur with powellite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaMoO₄
- Mohs hardness
- 3.5-4
- Density
- 4.26 g/cm³
- Streak
- Light yellow
- Luster
- Subadamantine, resinous, pearly
- Transparency
- Transparent to translucent
- Crystal system
- Tetragonal
- Crystal habit
- Crystalline, granular
- Cleavage
- {112}, {011}, {001}, all indistinct
- Fluorescence
- Yellow-white to golden yellow under SW UV; Yellow-white to golden yellow under LW UV
- Rarity
- Uncommon
- Uses
- Collector, Indicator mineral
- Host rock
- An uncommon secondary mineral, typically formed in the oxidation zone of molybdenum-bearing hydrothermal mineral deposits, rarely in basalts, tactites, and granite pegmatites
Where rockhounds find powellite
Classic worldwide localities
- Peacock Lode, Seven Devils district, Adams Co., Idaho, USA
- Isle Royale, Calumet & Hecla, Tamarack, and other mines, Houghton Co., Michigan, USA
- Pine Creek tungsten mine, near Bishop, Inyo Co., California, USA
- Tonopah-Divide mine, Divide district, Esmeralda Co., Nevada, USA
- Huepac, Sonora, Mexico
- Chuquicamata, Antofagasta, Chile
Field-hunting tip
Where it forms: An uncommon secondary mineral, typically formed in the oxidation zone of molybdenum-bearing hydrothermal mineral deposits, rarely in basalts, tactites, and granite pegmatites. If you start seeing molybdenite, ferrimolybdite, stilbite in float, you are in the right ground. Typical habit: crystalline, granular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify powellite?+
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Find powellite on the map
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