Cobaltite Identification Guide

What Cobaltite Looks Like

Cobaltite is a cobalt sulfarsenide (CoAsS) and a primary ore of cobalt. It has a bright metallic luster and a distinctive silver-white to reddish-silver color, sometimes with a faint pinkish or violet-steel tint. It commonly forms cubic, pyritohedral, or octahedral crystals (often with striated faces) resembling pyrite, as well as granular masses. Tarnished surfaces and associated pink erythrite ("cobalt bloom") coatings are useful clues.

Step-by-Step Field ID Checklist

1. Note metallic luster and color. Silver-white with a reddish or pinkish cast distinguishes it from yellow pyrite.
2. Look for cubic/pyritohedral crystals with striated faces.
3. Check for pink coatings. A pink-to-crimson erythrite bloom on the surface is a strong indicator of a cobalt mineral.
4. Test hardness. It is hard for a sulfide (Mohs ~5.5), scratching glass.
5. Take the streak. Grayish-black to black.
6. Heft it. It is heavy (high specific gravity ~6.3).

Key Diagnostic Tests

• Hardness: ~5.5 — harder than most sulfides; it scratches glass.
• Streak: Grayish-black to black.
• Density: High, ~6.0–6.3 g/cm³ — noticeably heavy.
• Cleavage: Imperfect cubic cleavage; uneven fracture, brittle.
• Associated mineral: Pink erythrite "cobalt bloom" on weathered surfaces.
• Caution: Contains arsenic — wash hands; avoid heating or inhaling dust.

Common Look-Alikes and How to Tell Them Apart

• Pyrite: Pyrite is brass-yellow (not silver-pink), gives a greenish-black streak, and is iron-sulfide; cobaltite's silvery-reddish color and any pink erythrite bloom set it apart.
• Arsenopyrite: Silver-white and similar hardness, but arsenopyrite is more steely-white, often gives a garlic odor when struck (arsenic), and lacks the cobalt-pink bloom; chemical tests distinguish them.
• Skutterudite / smaltite: Also silver-white cobalt-arsenic minerals; cobaltite tends toward more pinkish hue and cubic habit, but lab analysis may be needed.
• Galena: Galena is softer (2.5), has perfect cubic cleavage and a bright lead-gray streak, and is denser yet cleaves cleanly; cobaltite is harder and lacks galena's perfect cleavage.
• Marcasite: Pale, but iron sulfide with different streak.

Where It Is Found

Cobaltite occurs in high-temperature hydrothermal veins and contact metamorphic deposits, often with other cobalt-nickel-arsenic minerals, magnetite, and sulfides. Classic localities include Tunaberg and Håkansboda (Sweden), Cobalt (Ontario, Canada), Skutterud (Norway), and Bou Azzer (Morocco). Look in metalliferous vein systems and the pink-stained zones around cobalt deposits.