Identification guide · Igneous Rocks
How to Identify Peridotite
Peridotite is typically dark green to greenish-black and coarse-grained, dominated by olivine crystals that give it a granular, sugary texture, with pyroxene present as darker, blockier grains. It has an overall hardness around 6 to 7 reflecting its olivine content, no rock-scale cleavage, and it commonly shows signs of alteration to serpentine along fractures, producing a mottled or greasy green appearance. It is distinguished from basalt by its much coarser grain size and lack of feldspar, and from gabbro by its dominant olivine content and darker, more uniformly green color; heavily serpentinized peridotite can be mistaken for serpentinite itself.
Peridotite identification checklist
| Color | Green, Dark green, Yellowish green, Black | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous (olivine and pyroxene grains) | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Opaque | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 5.5–7 | It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. |
| Fracture | Uneven to conchoidal | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 3.1–3.4 | Heavier than it looks (specific gravity about 3.25). |
Extra tests for Peridotite
Glass check. Peridotite 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.
Peridotite look-alikes and how to tell them apart
Both sit near Mohs 5.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Peridotite vs Rainbow Obsidian →
Both sit near Mohs 5.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Peridotite vs Quartz →
Both sit near Mohs 5.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Peridotite vs Andesite →
Both sit near Mohs 5.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
Peridotite identification FAQ
How can you tell if a rock is Peridotite?
Check the color (green, dark green, yellowish green, and black), the vitreous (olivine and pyroxene grains) luster, a Mohs hardness of 5.5–7. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Peridotite?
Peridotite has a Mohs hardness of 5.5–7. 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 Peridotite and Rainbow Obsidian?
Peridotite (Mohs 5.5–7, vitreous (olivine and pyroxene grains) luster) and Rainbow Obsidian (Mohs 5.5, vitreous luster) look alike, but hardness, streak and heft usually separate them. See the full Peridotite vs Rainbow Obsidian comparison for a side-by-side table.
Is Peridotite worth anything?
Entry-level Peridotite 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 Peridotite?
Peridotite is most often green, dark green, yellowish green, and black. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
