Ferrimolybdite is a secondary oxidation product that typically forms as bright yellow, powdery, or fibrous crusts on weathering molybdenite. It is easily identified by its distinctive canary-yellow color and its common occurrence as a soil or vein coating in ore deposits.
Is this ferrimolybdite?
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 ferrimolybdite with a known reference. Ferrimolybdite sits at Mohs 1-2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Ferrimolybdite leaves a pale yellow streak.
- 3Read the lusterHold the specimen under a strong light. Ferrimolybdite typically shows a dull luster.
- 4Match the color rangeCompare against the expected color range: yellow, straw-yellow, canary-yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: fibrous, earthy, powdery, or as encrustations.
Often confused with
Ferrimolybdite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Ferrimolybdite leaves pale yellow, Molybdite leaves yellow; luster reads dull on Ferrimolybdite and silky on Molybdite.
How to tell apart: Streak differs — Ferrimolybdite leaves pale yellow, Jarosite leaves yellow; luster reads dull on Ferrimolybdite and vitreous on Jarosite.
How to tell apart: Luster reads dull on Ferrimolybdite and pearly on Autunite.
Often found alongside ferrimolybdite
Minerals reported to co-occur with ferrimolybdite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₂³⁺(MoO₄)₃·8H₂O
- Mohs hardness
- 1-2
- Density
- 3.0-3.5 g/cm³
- Streak
- Pale Yellow
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Fibrous, Earthy, Powdery, Or as Encrustations
- Cleavage
- None
- Rarity
- Common
- Uses
- Collector, Indicator Mineral
- Host rock
- Oxidized Zones of Molybdenum-bearing Hydrothermal Deposits
- Typical price
- $10-60 for small mineral specimens
Where rockhounds find ferrimolybdite
Classic worldwide localities
- Climax, Colorado, USA
- Questa, New Mexico, USA
- Azegour, Morocco
- Kounrad, Kazakhstan
- Altai Mountains, Russia
Field-hunting tip
Look in oxidized zones of molybdenum-bearing hydrothermal deposits country — that is the host setting where ferrimolybdite typically forms. If you start seeing molybdenite, limonite, quartz in float, you are in the right ground. Field specimens usually show a fibrous, earthy, powdery, or as encrustations habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferrimolybdite?+
Where is ferrimolybdite found?+
How much is ferrimolybdite worth?+
What rocks look like ferrimolybdite?+
What minerals are found with ferrimolybdite?+
What kind of rock does ferrimolybdite form in?+
What is ferrimolybdite used for?+
Find ferrimolybdite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
