Uraninite Identification Guide

Safety First

Uraninite is radioactive and contains uranium. Handle minimally, never inhale dust, store sealed away from living spaces, wash hands after contact, and never tumble, grind, or cut it. A Geiger counter is the most reliable field tool for this mineral.

What Uraninite Looks Like

Uraninite (massive variety called pitchblende) is a uranium oxide, typically black to brownish-black or steel-gray, with a greasy, pitchy, dull-to-submetallic luster. Crystals (rare) are cubic or octahedral; far more common is massive, botryoidal (grape-like), or banded "pitchblende" with a kidney-shaped surface. It is notably heavy for its size. Weathered surfaces may show yellow, orange, or green secondary uranium minerals (uranophane, autunite, gummite) - a strong supporting clue.

Step-by-Step Field-ID Checklist

1. Heft it (carefully). Extreme density is the first giveaway - it feels far heavier than ordinary black rock.
2. Note the color and luster. Black/steel-gray with a pitchy, greasy shine.
3. Look for botryoidal/banded form rather than well-formed crystals.
4. Scan for yellow/orange/green alteration crusts of secondary uranium minerals.
5. Use a Geiger counter. Strong radioactivity confirms it; this is the decisive test.
6. Streak test (with care, then clean up): brownish-black to grayish.

Key Diagnostic Tests

• Mohs hardness: ~5-6.
• Streak: Brownish-black, gray, or olive.
• Cleavage/fracture: No cleavage; conchoidal to uneven fracture.
• Magnetism: None to negligible.
• Radioactivity: Strongly radioactive - THE diagnostic property.
• Density: Very high, ~8-10 g/cm3 for pure crystalline material (lower, ~6.5-9, for massive pitchblende). Few minerals this color are this heavy.

Common Look-Alikes

• Magnetite: Black and heavy but strongly magnetic and NOT radioactive.
• Hematite (massive): Reddish-brown streak, not radioactive.
• Goethite/limonite: Yellow-brown streak, lower density, not radioactive.
• Coal/obsidian: Far lighter, not radioactive.
• Columbite/cassiterite: Heavy but only weakly (if at all) radioactive and with different streak.

Radioactivity plus very high density plus black pitchy luster is conclusive; the magnet quickly rules out magnetite.

Where It Is Found

Uraninite occurs in granitic pegmatites, high-temperature hydrothermal veins, and unconformity-type uranium deposits. Major localities include the Athabasca Basin (Canada), the Erzgebirge (Germany/Czechia, where pitchblende was first described), Shinkolobwe (DR Congo), Australia, and various US pegmatites and vein deposits.