Where is Greenschist found?
Metamorphic rock (Greenschist facies)
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Open the appGreenschist occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Greenschist
Appalachian Mountains, USA
Extensive exposures of greenschist facies rocks are found throughout the Appalachian orogen, particularly in the Piedmont and Blue Ridge provinces.
Scottish Highlands, UK
Part of the Caledonian orogeny, the Scottish Highlands contain significant greenschist occurrences, particularly in areas of metamorphosed mafic volcanic rocks.
Fennoscandian Shield, Scandinavia
Ancient Precambrian shield areas, such as the Fennoscandian Shield, host vast tracts of greenschist facies rocks, often associated with greenstone belts.
Western Alps, Europe
Metamorphic complexes in the Western Alps, particularly in the Penninic nappes, show greenschist facies metamorphism of former oceanic crust and continental margin sediments.
Canadian Shield, Canada
Large areas of the Canadian Shield, especially within greenstone belts, are composed of greenschist facies rocks, often associated with significant mineral deposits.
Collecting tips
- Look for Green Coloration. The most obvious indicator is the green color, which can range from pale to dark green. This is due to the presence of chlorite, actinolite, and epidote.
- Check for Schistosity. Greenschist exhibits a distinct schistose texture, meaning it will break along parallel planes due to the alignment of platy minerals. This gives it a layered or foliated appearance.
- Examine Mineral Assemblage. Identify the characteristic minerals: chlorite (soft, green, flaky), actinolite (green, needle-like or fibrous), epidote (pistachio green), albite (white, dull), and quartz (glassy). A hand lens can be very helpful.
- Consider Geological Context. Greenschist is typically found in regionally metamorphosed terrains, often associated with ancient mountain belts or shield areas. Look for it in areas mapped as metamorphic complexes.
- Test Hardness (Carefully). Chlorite is relatively soft (Mohs 2-2.5), so a greenschist containing abundant chlorite will be softer than many other metamorphic rocks. However, quartz and actinolite will be harder.
Quick Check
- Color:
- Green (various shades)
- Luster:
- Dull to sub-vitreous, sometimes silky on foliation surfaces
- Streak:
- White to pale green
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