Identification guide · Minerals
How to Identify Cobaltite
Cobaltite typically forms crystals that look cubic at a glance but actually belong to the orthorhombic system, with faces sometimes showing fine striations that reveal the lower symmetry. Its color is silvery white to gray with a distinctive pinkish cast, its luster is metallic, and its streak is grayish black. Hardness of 5.5 helps distinguish it from softer sulfides, while its arsenic content gives a faint garlic odor when freshly broken or struck, a classic field test shared with arsenopyrite, which cobaltite otherwise closely resembles.
Cobaltite identification checklist
| Color | Silvery white with pink/reddish tint, Steel gray | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Metallic | Turn it under a lamp: a true metallic shine reflects like polished metal and stays opaque at thin edges. |
| Transparency | Opaque | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 5.5 | It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. |
| Streak | Grayish black | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Perfect cubic, three directions | |
| Fracture | Uneven | |
| Specific gravity | 6.0–6.3 | Very heavy, metallic heft (specific gravity about 6.15). |
| Crystal system | Orthorhombic (pseudo-cubic) |
Cobaltite look-alikes and how to tell them apart
Both sit near Mohs 5.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Cobaltite vs Arsenopyrite →
Cobaltite is harder (Mohs 5.5) than Bismuth (Mohs 2–2.5), so Cobaltite will scratch Bismuth and not the other way round. A fingernail (Mohs 2.5) scratches it easily. Cobaltite vs Bismuth →
Both sit near Mohs 5.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Cobaltite vs Hematite →
Andalusite is harder (Mohs 6.5–7.5) than Cobaltite (Mohs 5.5), so Andalusite will scratch Cobaltite and not the other way round. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
Cobaltite identification FAQ
How can you tell if a rock is Cobaltite?
Check the color (silvery white with pink/reddish tint and steel gray), the metallic luster, a Mohs hardness of 5.5 and a grayish black streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Cobaltite?
Cobaltite has a Mohs hardness of 5.5. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
What is the difference between Cobaltite and Arsenopyrite?
Cobaltite (Mohs 5.5, metallic luster) and Arsenopyrite (Mohs 5.5–6, metallic luster) look alike, but hardness, streak and heft usually separate them. See the full Cobaltite vs Arsenopyrite comparison for a side-by-side table.
Is Cobaltite worth anything?
Entry-level Cobaltite specimens sell for around $2, typical collector pieces about $20, and premium examples $150 or more depending on size, quality and locality.
What color is Cobaltite?
Cobaltite is most often silvery white with pink/reddish tint and steel gray. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
