Greenschist
Greenschist is a greenish metamorphic rock named for its common green minerals and schistose texture. It often looks green, gray-green, or dark green and may have a silky sheen.
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Greenschist properties at a glance
| Type | Metamorphic Rocks |
|---|---|
| Chemical formula | Chlorite, actinolite, epidote, and albite-rich metamorphic rock |
| Mohs hardness | 4.5 |
| Luster | silky |
| Streak | Variable; usually pale greenish gray |
| Cleavage | Variable by mineral grains |
| Fracture | Uneven to splintery |
| Specific gravity | 2.9 |
| Transparency | opaque |
| Common colors | Green, Gray green, Dark green, Black, White |
| Rarity | common |
Geology & background
Forms during low to medium grade metamorphism, commonly of basaltic rocks, producing green minerals such as chlorite, actinolite, and epidote.
Greenschist helps geologists recognize low to medium grade metamorphism and altered volcanic or mafic source rocks.
How to identify Greenschist
- 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.
Where Greenschist is found
Reported from multiple metamorphic terrains worldwide; verify locality against specimen provenance when available.
How much is Greenschist worth?
| Entry-level specimen | $1 |
|---|---|
| Typical collector specimen | $10 |
| Premium specimen | $75+ |
Greenschist is usually valued for teaching, field context, locality, texture, mineral content, or unusually attractive specimens rather than high gem value.
Common uses
- Field identification
- Metamorphic grade study
- Education
- Decorative stone when durable
Interesting facts
- Greenschist color commonly comes from chlorite, actinolite, or epidote.
- It represents lower metamorphic grade than amphibolite.
- Some greenschists split along foliated surfaces.
Care & safety
Greenschist can vary in toughness, cleavage, and weathering depending on mineral mix and fabric.
Avoid inhaling dust. Do not cut, grind, or polish unknown metamorphic rocks without eye protection and a properly rated respirator.
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