Identification guide · Metamorphic Rocks
How to Identify Greenschist
Greenschist is usually green, gray green, and dark green with a silky luster and is opaque. It has a Mohs hardness of 4.5. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Its streak is variable; usually pale greenish gray. It is most often confused with Blueschist, Mylonite, and Actinolite; the tests below separate them.
Greenschist identification checklist
| Color | Green, Gray green, Dark green, Black, White | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Silky | Compare a fresh surface with glass and metal; this luster is softer than either. |
| Transparency | Opaque | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 4.5 | A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. |
| Streak | Variable; usually pale greenish gray | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Variable by mineral grains | |
| Fracture | Uneven to splintery | |
| Specific gravity | 2.9 | Ordinary rock-like heft (specific gravity about 2.9), similar to quartz. |
Greenschist look-alikes and how to tell them apart
Blueschist is harder (Mohs 5.5) than Greenschist (Mohs 4.5), so Blueschist will scratch Greenschist and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Greenschist vs Blueschist →
Mylonite is harder (Mohs 5.5) than Greenschist (Mohs 4.5), so Mylonite will scratch Greenschist and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Greenschist vs Mylonite →
Actinolite is harder (Mohs 5–6) than Greenschist (Mohs 4.5), so Actinolite will scratch Greenschist and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Greenschist vs Actinolite →
Greenschist is harder (Mohs 4.5) than Phyllite (Mohs 2.5–4), so Greenschist will scratch Phyllite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Greenschist vs Phyllite →
Field tips
- Look for green to gray-green color with fine to medium foliation.
- A silky or slightly shiny surface can come from aligned chlorite or actinolite.
- Greenschist is usually greener and lower grade than amphibolite.
- Weathered surfaces may look dull brown or gray, so check a fresh surface when possible.
Greenschist identification FAQ
How can you tell if a rock is Greenschist?
Check the color (green, gray green, dark green, and black), the silky luster, a Mohs hardness of 4.5 and a variable; usually pale greenish gray streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Greenschist?
Greenschist has a Mohs hardness of 4.5. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not.
What is the difference between Greenschist and Blueschist?
Greenschist (Mohs 4.5, silky luster) and Blueschist (Mohs 5.5, silky luster) look alike, but hardness, streak and heft usually separate them. See the full Greenschist vs Blueschist comparison for a side-by-side table.
Is Greenschist worth anything?
Entry-level Greenschist 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 Greenschist?
Greenschist is most often green, gray green, dark green, and black. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
