metamorphic
Greenstone / River Siltstone
Metasedimentary Greenstone (Chlorite-rich Siltstone)
Hardness: 5.5-6.5 (Mohs scale), Color: Sage green to grayish-green, Luster: Dull/Earthy when dry, Waxy/Satiny when wet, Crystal Structure: Microcrystalline, Cleavage: Poor to none due to weathering, Specific Gravity: 2.7–3.0
- Hardness
- 5
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Physical properties
Hardness: 5.5-6.5 (Mohs scale), Color: Sage green to grayish-green, Luster: Dull/Earthy when dry, Waxy/Satiny when wet, Crystal Structure: Microcrystalline, Cleavage: Poor to none due to weathering, Specific Gravity: 2.7–3.0
Formation & geological history
Formed through low-grade metamorphism of sedimentary silt or volcanic ash (greenschist facies). This specific specimen has been further shaped by fluvial (river) erosion, resulting in its smooth, oval, water-worn cobble shape.
Uses & applications
Used in decorative landscaping, as 'worry stones', or historically for stone tools and celts due to its toughness. Fine-grained varieties are sometimes used for small carvings or beads.
Geological facts
The green color is primarily derived from the presence of minerals like chlorite, epidote, or actinolite. Greenstone belts are home to some of the oldest known rocks on Earth, some dating back over 2.5 billion years.
Field identification & locations
Identify in the field by its distinct dull green hue and smooth, rounded texture compared to surrounding gray rocks. It will not scratch easily with a copper penny but can be scratched by a steel file. Commonly found in glacial till and riverbeds in regions with volcanic or metamorphic history.
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