Gadolinite-(Ce) is a rare-earth silicate mineral typically found in granitic pegmatites. It is often distinguished by its dark, almost pitch-black appearance and vitreous luster, though it is frequently altered by radioactive decay into an amorphous state. Collectors look for well-defined, prismatic crystals, though the material is most commonly found in massive or granular form.
Is this gadolinite-(ce)?
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 gadolinite-(ce) with a known reference. Gadolinite-(Ce) sits at Mohs 6.5-7, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: greenish gray.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: metamict.
Often confused with
Gadolinite-(Ce) vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Gadolinite-(Ce) leaves greenish gray, Allanite leaves gray; luster reads vitreous on Gadolinite-(Ce) and submetallic on Allanite.
How to tell apart: Streak differs, so Gadolinite-(Ce) leaves greenish gray, Euxenite-(Y) leaves yellowish, grayish, or reddish brown; luster reads vitreous on Gadolinite-(Ce) and brilliant submetallic, waxy to resinous on fractures on Euxenite-(Y).
Often found alongside gadolinite-(ce)
Minerals reported to co-occur with gadolinite-(ce). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ce₂FeBe₂Si₂O₁₀
- Mohs hardness
- 6.5-7
- Density
- 4.20 g/cm³
- Colors
- Streak
- Greenish gray
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Metamict
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Source of rare earth elements
- Host rock
- In syenite pegmatite veins along a contact between basalt and monzonite
Where rockhounds find gadolinite-(ce)
Classic worldwide localities
- From a dump at Buer, nine km southeast of Skien, Bjorkendalen region, and in the Bakken quarry, Tvedalen, Norway (type locality)
Field-hunting tip
Where it forms: In syenite pegmatite veins along a contact between basalt and monzonite. If you start seeing aegirine, pyrochlore, zircon in float, you are in the right ground. Typical habit: metamict. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify gadolinite-(ce)?+
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Is gadolinite-(ce) safe to handle?+
What rocks look like gadolinite-(ce)?+
What minerals are found with gadolinite-(ce)?+
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Find gadolinite-(ce) on the map
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