Gadolinite-(Y) is a rare silicate mineral primarily found in rare-element pegmatites. It typically occurs as dark, glassy prismatic crystals that often exhibit a brownish-green color when viewed in thin splinters under bright light.
Is this gadolinite-(y)?
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-(y) with a known reference. Gadolinite-(Y) 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 to greasy.
- 4Match the color rangeCompare against the expected color range: black, brown, green, green black, light green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: crystalline, massive, prismatic.
Often confused with
Gadolinite-(Y) vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Gadolinite-(Y) leaves greenish gray, Allanite leaves gray; luster reads vitreous to greasy on Gadolinite-(Y) and submetallic on Allanite.
How to tell apart: Streak differs, so Gadolinite-(Y) leaves greenish gray, Euxenite-(Y) leaves yellowish, grayish, or reddish brown; luster reads vitreous to greasy on Gadolinite-(Y) and brilliant submetallic, waxy to resinous on fractures on Euxenite-(Y).
Often found alongside gadolinite-(y)
Minerals reported to co-occur with gadolinite-(y). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Y₂Fe²⁺Be₂Si₂O₁₀
- Mohs hardness
- 6.5-7
- Density
- 4.36-4.77 g/cm³
- Colors
- Streak
- Greenish gray
- Luster
- Vitreous to greasy
- Transparency
- Opaque, nearly transparent in thin fragments
- Crystal system
- Monoclinic
- Crystal habit
- Crystalline, massive, prismatic
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Source of rare earth elements
- Host rock
- In granite and alkalic granite pegmatites
Where rockhounds find gadolinite-(y)
Classic worldwide localities
- Clear Creek pegmatite, Burnet Co., and the Baringer Hill pegmatite, 26 km west of Burnet, and at Rode Ranch, near Bluffton, Llano Co., Texas, USA
- Hackberry, Mohave Co., Arizona, USA
- Devil's Head Mountain, Douglas Co., and near Lake George, Park Co., Colorado, USA
- Hitterö Island, Flekkefjord, Norway
- Slobrekka and Dauren, Iveland, Norway
Field-hunting tip
Where it forms: In granite and alkalic granite pegmatites. If you start seeing allanite, fluorite, fergusonite in float, you are in the right ground. Typical habit: crystalline, massive, prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify gadolinite-(y)?+
Where is gadolinite-(y) found?+
Is gadolinite-(y) safe to handle?+
What rocks look like gadolinite-(y)?+
What minerals are found with gadolinite-(y)?+
What kind of rock does gadolinite-(y) form in?+
What is gadolinite-(y) used for?+
Find gadolinite-(y) on the map
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