Formanite-(Y) is a rare yttrium tantalate mineral found primarily in granitic pegmatites. Collectors look for its characteristic brown to black prismatic crystals, which are often metamict due to internal radiation damage over geological time.
Is this formanite-(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 formanite-(y) with a known reference. Formanite-(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: pale yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic, resinous to greasy; weathered surfaces are dull.
- 4Match the color rangeCompare against the expected color range: brownish black, black.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: metamict, tabular.
Often confused with
Formanite-(Y) vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Formanite-(Y) leaves pale yellow, Fergusonite-(Y) leaves brown, yellow-brown, greenish gray; luster reads metallic, resinous to greasy; weathered surfaces are dull on Formanite-(Y) and dull; vitreous to submetallic on fractures on Fergusonite-(Y).
How to tell apart: Streak differs, so Formanite-(Y) leaves pale yellow, Samarskite-(Y) leaves dark reddish brown to black, yellow-brown; gray when altered; luster reads metallic, resinous to greasy; weathered surfaces are dull on Formanite-(Y) and vitreous to resinous, may be submetallic, splendent; externally dull on Samarskite-(Y).
How to tell apart: Streak differs, so Formanite-(Y) leaves pale yellow, Columbite leaves blackish brown; luster reads metallic, resinous to greasy; weathered surfaces are dull on Formanite-(Y) and submetallic on Columbite.
Often found alongside formanite-(y)
Minerals reported to co-occur with formanite-(y). Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- YTaO₄
- Mohs hardness
- 5.5-6.5
- Density
- 6.17-6.24 g/cm³
- Colors
- Streak
- Pale yellow
- Luster
- Metallic, resinous to greasy; weathered surfaces are dull
- Transparency
- Opaque, thin fragments may be transparent
- Crystal system
- Tetragonal
- Crystal habit
- Metamict, tabular
- Cleavage
- {111}, interrupted
- Rarity
- Rare
- Uses
- Collector, Geological study
- Host rock
- In granites and albitized, RE-rich pegmatitic veins; a detrital mineral in placers
Where rockhounds find formanite-(y)
Classic worldwide localities
- Found at Cooglegong, Pilbara district, and in the Marble Bar district, Western Australia
- Mt. Ploskaya, Western Keivy area, Kola Peninsula, and an undisclosed location in Siberia, Russia
- Occurs at an undisclosed locality in Jiangxi Province, China
Field-hunting tip
Where it forms: In granites and albitized, RE-rich pegmatitic veins; a detrital mineral in placers. If you start seeing cassiterite, monazite, euxenite in float, you are in the right ground. Typical habit: metamict, tabular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify formanite-(y)?+
Where is formanite-(y) found?+
Is formanite-(y) safe to handle?+
What rocks look like formanite-(y)?+
What minerals are found with formanite-(y)?+
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Find formanite-(y) on the map
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