Euxenite Identification Guide
Identify euxenite, a black radioactive niobium-tantalum-titanium rare-earth oxide, by its metamict character, high density, and pegmatite setting.
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What Euxenite Looks Like
Euxenite-(Y) is a complex oxide of niobium, tantalum, titanium, and yttrium/rare earths found in granite pegmatites. It is a radioactive, often metamict (radiation-amorphized) mineral.
- Color: black to brownish-black; weathered surfaces may show yellow-brown or greenish alteration crusts.
- Luster: submetallic to brilliant/greasy resinous; vitreous on fresh fracture.
- Transparency: opaque.
- Habit: prismatic crystals, but usually massive or as irregular grains; commonly metamict, so crystal faces may be rounded.
Step-by-Step Field-ID Checklist
- Note color and luster. A heavy black mineral with a greasy submetallic shine in pegmatite is a candidate.
- Heft it. It feels distinctly heavy for its size.
- Test radioactivity. A Geiger counter reads elevated counts; this is a strong indicator (handle and store safely).
- Check streak. Streak is yellowish-brown to grayish-brown, not black like magnetite.
- Look for conchoidal fracture and a pitchy luster typical of metamict oxides.
Key Diagnostic Tests
- Mohs hardness: ~5.5-6.5.
- Streak: yellowish to reddish-brown / grayish-brown.
- Cleavage/fracture: no good cleavage; conchoidal to subconchoidal fracture, brittle.
- Specific gravity: high, ~4.3-5.9 (varies with composition and metamictization).
- Radioactivity: moderately to strongly radioactive (U and Th); a key diagnostic. Store away from living spaces and wash hands.
- Non-magnetic to weakly magnetic (unlike strongly magnetic magnetite).
Common Look-Alikes and How to Tell Them Apart
- Magnetite/ilmenite: magnetite is strongly magnetic with a black streak and is not radioactive; euxenite gives a brown streak and is radioactive.
- Columbite-tantalite: also heavy black pegmatite oxides, but typically not as radioactive and have a more submetallic, sometimes iridescent look; lab analysis distinguishes them.
- Samarskite/fergusonite/aeschynite: very similar black radioactive REE-oxides; reliable separation needs XRD or chemical analysis.
- Allanite: lower density, brown, weakly radioactive, occurs more in granites and skarns.
Where It Is Typically Found
Euxenite occurs in granitic pegmatites and rare-earth-bearing placers. Notable sources include Norway (the type region), Madagascar, Australia, Canada, and the western United States. It has been mined as a minor ore of niobium, tantalum, titanium, and rare earths.
Frequently asked questions
Is euxenite radioactive?
Yes. Euxenite contains uranium and thorium and is moderately to strongly radioactive, often metamict. Handle it briefly, store it away from living areas in a ventilated container, and wash your hands afterward.
How can you tell euxenite from magnetite?
Magnetite is strongly magnetic with a black streak and is not radioactive. Euxenite has a brown to grayish-brown streak, a greasy submetallic luster, and registers on a Geiger counter.
What is euxenite used for?
It is a minor ore of niobium, tantalum, titanium, and rare-earth elements (especially yttrium), recovered chiefly from pegmatites and placer concentrates.
Why does euxenite have rounded crystals?
Self-irradiation from its uranium and thorium destroys the internal crystal structure over geologic time (metamictization), so crystals become amorphous and faces look rounded or glassy with conchoidal fracture.