metamorphic

Greenstone with rusty mineral patches

Greenstone (metamorphosed mafic volcanic rock; likely chlorite–epidote–actinolite assemblage)

AI-generated identification · may be incorrect

Fine-grained, dark green, rounded specimen with scattered orange-brown iron-oxide staining. Typical greenstone hardness is about 5–6 Mohs; usually dull to slightly waxy, with no visible cleavage and a massive texture.

Identified September 27, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms when basalt or other mafic volcanic rock is altered by low-grade metamorphism and hydrothermal fluids. This process occurs across many geologic ages, commonly in ancient volcanic belts and oceanic crust.

Uses & applications

Primarily collected as a field specimen or used decoratively; some greenstone is carved or polished, and large deposits have limited aggregate uses.

Geological facts

The green color commonly comes from chlorite, epidote, or actinolite; rusty spots may reflect oxidation of iron-bearing minerals.

Field identification & locations

Look for a dense, fine-grained green rock, often with pale or rusty patches; the image alone cannot confirm its exact mineralogy. Greenstones occur in metamorphic belts worldwide, including the Canadian Shield and other ancient cratons.