metamorphic
Greenstone
Metabasalt / Chlorite Schist
Hardness: 6-7 on Mohs scale; Color: Dull green, dark forest green to grayish-green; Luster: Earthy to waxy; Crystal Structure: Very fine-grained, microcrystalline; Cleavage: None (subconchoidal fracture); Specific Gravity: 2.8-3.0
- Hardness
- 6-7 on Mohs scale
- Color
- Dull green, dark forest green to grayish-green
- Luster
- Earthy to waxy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dull green, dark forest green to grayish-green; Luster: Earthy to waxy; Crystal Structure: Very fine-grained, microcrystalline; Cleavage: None (subconchoidal fracture); Specific Gravity: 2.8-3.0
Formation & geological history
Formed through the low-grade metamorphism (greenschist facies) of mafic igneous rocks like basalt. Subjected to heat and pressure, original minerals transform into chlorite, actinolite, and epidote. Often associated with ancient oceanic crust or mountain-building events.
Uses & applications
Historically used for making stone axes and tools due to its toughness. Today used as crushed stone for road construction, architectural stone accents, ornate carvings, and decorative gravel.
Geological facts
The green color is primarily due to the presence of chlorite, actinolite, and epidote. In some regions like British Columbia and New Zealand, high-quality greenstone is referred to as 'Pounamu' and holds great cultural significance.
Field identification & locations
Identify in the field by its distinct green hue, extreme toughness, and lack of obvious layering compared to slate. Commonly found in coastal areas, river beds near tectonic plate boundaries, and ancient mountain belts.
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