Fergusonite-(Y) is a rare earth niobate mineral typically found as prismatic crystals in granite pegmatites. It is almost always found in a metamict state, where radioactive decay has disrupted its original crystal lattice, resulting in a dark, glassy appearance.
Is this fergusonite-(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 fergusonite-(y) with a known reference. Fergusonite-(Y) sits at Mohs 5.5-6.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brown, yellow-brown, greenish gray.
- 3Read the lusterHold the specimen under a strong light. Luster: dull; vitreous to submetallic on fractures.
- 4Match the color rangeCompare against the expected color range: black, brown, gray, yellow.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: metamict, prismatic.
Often confused with
Fergusonite-(Y) vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Fergusonite-(Y) leaves brown, yellow-brown, greenish gray, Euxenite-(Y) leaves yellowish, grayish, or reddish brown; luster reads dull; vitreous to submetallic on fractures on Fergusonite-(Y) and brilliant submetallic, waxy to resinous on fractures on Euxenite-(Y).
How to tell apart: Streak differs, so Fergusonite-(Y) leaves brown, yellow-brown, greenish gray, Columbite leaves blackish brown; luster reads dull; vitreous to submetallic on fractures on Fergusonite-(Y) and submetallic on Columbite.
Often found alongside fergusonite-(y)
Minerals reported to co-occur with fergusonite-(y). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- YNbO₄
- Mohs hardness
- 5.5-6.5
- Density
- 5.6-5.8 g/cm³
- Streak
- Brown, yellow-brown, greenish gray
- Luster
- Dull; vitreous to submetallic on fractures
- Transparency
- Opaque, transparent on thin edges
- Crystal system
- Tetragonal
- Crystal habit
- Metamict, prismatic
- Cleavage
- {111}, poor
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Typical of rare-earth-bearing granite pegmatites; in placers
Where rockhounds find fergusonite-(y)
Classic worldwide localities
- Baringer Hill pegmatite, 26 km west of Burnet, Llano Co., Texas, USA
- Champion and Rutherford pegmatite deposits, Amelia Co., and at Little Friar Mountain, Amherst Co., Virginia, USA
- Spruce Pine, Mitchell Co., North Carolina, USA
- Storeville, Anderson Co., South Carolina, USA
- Arendal, Norway
- Berg, near Råde, Norway
Field-hunting tip
Where it forms: Typical of rare-earth-bearing granite pegmatites; in placers. If you start seeing monazite, gadolinite, thalenite in float, you are in the right ground. Typical habit: metamict, prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify fergusonite-(y)?+
Where is fergusonite-(y) found?+
Is fergusonite-(y) safe to handle?+
What rocks look like fergusonite-(y)?+
What minerals are found with fergusonite-(y)?+
What kind of rock does fergusonite-(y) form in?+
What is fergusonite-(y) used for?+
Find fergusonite-(y) on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
