Identification guide · Igneous Rocks
How to Identify Dunite
Dunite is a granular, typically olive-green to yellowish-green rock composed almost entirely of olivine, with a vitreous luster on fresh grain faces and a white to pale streak. It has a hardness around 6.5 to 7, reflecting olivine's own hardness, and breaks with a conchoidal fracture since olivine lacks distinct cleavage. Weathered surfaces often show a reddish-brown or serpentinized greenish rind that contrasts with the fresher green interior. It can be mistaken for other ultramafic rocks like peridotite, which carries more pyroxene.
Dunite identification checklist
| Color | Olive green, Yellowish green, Dark green, Brown (weathered) | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous (olivine grains) | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Opaque (translucent in thin section) | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 6.5–7 | It scratches glass and a steel knife and cannot be scratched by a steel file. |
| Fracture | Conchoidal to uneven | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 3.2–3.3 | Heavier than it looks (specific gravity about 3.25). |
Extra tests for Dunite
Glass check. Dunite shares a glassy luster and conchoidal fracture with man-made glass. Glass sits near Mohs 5.5 and often contains round gas bubbles, so a hardness test and a hand lens separate them.
Dunite look-alikes and how to tell them apart
Both sit near Mohs 6.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Dunite vs Quartz →
Dunite is harder (Mohs 6.5–7) than Obsidian (Mohs 5.5), so Dunite will scratch Obsidian 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. Dunite vs Obsidian →
Dunite is harder (Mohs 6.5–7) than Rainbow Obsidian (Mohs 5.5), so Dunite will scratch Rainbow Obsidian 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. Dunite vs Rainbow Obsidian →
Both sit near Mohs 6.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
Dunite identification FAQ
How can you tell if a rock is Dunite?
Check the color (olive green, yellowish green, dark green, and brown (weathered)), the vitreous (olivine grains) luster, a Mohs hardness of 6.5–7. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Dunite?
Dunite has a Mohs hardness of 6.5–7. It scratches glass and a steel knife and cannot be scratched by a steel file.
What is the difference between Dunite and Quartz?
Dunite (Mohs 6.5–7, vitreous (olivine grains) luster) and Quartz (Mohs 7, vitreous, greasy on fracture surfaces luster) look alike, but hardness, streak and heft usually separate them. See the full Dunite vs Quartz comparison for a side-by-side table.
Is Dunite worth anything?
Entry-level Dunite specimens sell for around $1, typical collector pieces about $10, and premium examples $75 or more depending on size, quality and locality.
What color is Dunite?
Dunite is most often olive green, yellowish green, dark green, and brown (weathered). Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
