Ilsemannite is a rare, water-soluble molybdenum oxide typically found as a bright blue or deep blue-black powdery coating on other minerals. It is known for its intense color, which often fades or changes upon exposure to dry air. Collectors usually keep it in sealed containers to prevent dehydration and loss of its distinctive blue coloration.
Is this ilsemannite?
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 ilsemannite with a known reference. Ilsemannite sits at Mohs 5.5-6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale blue.
- 3Read the lusterHold the specimen under a strong light. Luster: dull.
- 4Match the color rangeCompare against the expected color range: blue, blue black, black.
- 5Look at form & habitCrystal system: amorphous. Typical habit: earthy.
Often confused with
Ilsemannite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Ilsemannite is noticeably harder (Mohs 5.5-6 vs. 3-4); streak differs, so Ilsemannite leaves pale blue, Molybdite leaves white; luster reads dull on Ilsemannite and adamantine on Molybdite.
How to tell apart: Ilsemannite is noticeably harder (Mohs 5.5-6 vs. 1.5-2); streak differs, so Ilsemannite leaves pale blue, Vivianite leaves white, altering to dark blue, brown; luster reads dull on Ilsemannite and vitreous, pearly on the cleavage, dull when earthy on Vivianite.
Often found alongside ilsemannite
Minerals reported to co-occur with ilsemannite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mo₃O₈·nH₂O
- Mohs hardness
- 5.5-6
- Colors
- Streak
- Pale blue
- Luster
- Dull
- Transparency
- Translucent
- Crystal system
- Amorphous
- Crystal habit
- Earthy
- Cleavage
- Good
- Rarity
- Uncommon
- Uses
- Collector, Indicator mineral
- Host rock
- A secondary mineral formed by the oxidation of molybdenum-bearing minerals
Where rockhounds find ilsemannite
1 mapped spotsClassic worldwide localities
- Marysvale, Ohio district, Piute Co., Utah, USA
- Kiggins mine, about 80 km southeast of Portland, Clackamas Co., Oregon, USA
- Quinn Draw, Shannon Co., and in the Runge mine, about 10 km north of Edgemont, Fall River Co., South Dakota, USA
- Six km west of Gibson, Shasta Co., and in the Kern River Canyon district, Kern Co., California, USA
- Bleiberg, Carinthia, Austria
- Himmelsfürst mine, Erbisdorf, near Freiberg, Saxony, Germany
Field-hunting tip
Where it forms: A secondary mineral formed by the oxidation of molybdenum-bearing minerals. If you start seeing jordisite, molybdenite, molybdite in float, you are in the right ground. Typical habit: earthy. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Wyoming. Start trip planning there.
Common questions
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Find ilsemannite on the map
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