Where is Greenstone found?
Metabasalt or Metavolcanic Rock
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Open the appGreenstone 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 Greenstone
Archean Greenstone Belts (Canada)
The Abitibi Greenstone Belt in the Canadian Shield (Ontario and Quebec) is one of the largest and best-preserved Archean greenstone belts globally, renowned for its gold and base metal deposits.
Archean Greenstone Belts (Australia)
The Yilgarn Craton in Western Australia contains numerous Archean greenstone belts (e.g., Kalgoorlie, Norseman-Wiluna) famous for their gold mineralization.
Archean Greenstone Belts (South Africa)
The Barberton Greenstone Belt (Kaapvaal Craton) is one of the oldest and best-exposed greenstone belts, known for its well-preserved volcanic and sedimentary rocks and early life forms.
Appalachian Mountains (USA)
Metamorphosed mafic volcanic rocks, including greenstone, are found in various terranes within the Appalachian Orogen, particularly in areas that experienced greenschist facies metamorphism.
Collecting tips
- Look for Green Color. The most obvious characteristic is its green color. Look for dark green, fine-grained rocks in areas known for ancient volcanic activity and metamorphism.
- Check for Relict Textures. In less deformed greenstones, look for relict volcanic textures such as pillow lavas (rounded, bulbous forms) or amygdales (gas bubbles filled with secondary minerals like quartz or calcite).
- Assess Hardness. Greenstone is generally tough and hard (Mohs 5-6), resisting scratching with a knife. This distinguishes it from softer, serpentinized rocks.
- Examine for Foliation. While some greenstones are massive, many exhibit a subtle to strong foliation (schistosity) due to the alignment of chlorite and actinolite. This can be seen as parallel planes of weakness or a preferred orientation of mineral grains.
- Geological Context. Greenstone is typically found in ancient cratonic regions, often associated with other metamorphosed volcanic and sedimentary rocks in 'greenstone belts'.
Quick Check
- Color:
- Dark green to greenish-black
- Luster:
- Dull to sub-vitreous
- Streak:
- Greenish-white to light green
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