metamorphic
Greenstone
Metabasalt / Chlorite Schist
Hardness: 6.0-7.0 (Mohs); Color: Dark green, dull grayish-green, or olive; Luster: Dull to sub-vitreous; Crystal Structure: Microcrystalline with occasional larger phenocrysts; Specific Gravity: 2.85-3.0; No distinct cleavage.
- Hardness
- 6
- Color
- Dark green, dull grayish-green, or olive
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6.0-7.0 (Mohs); Color: Dark green, dull grayish-green, or olive; Luster: Dull to sub-vitreous; Crystal Structure: Microcrystalline with occasional larger phenocrysts; Specific Gravity: 2.85-3.0; No distinct cleavage.
Formation & geological history
Formed through the low-grade metamorphism of mafic igneous rocks (such as basalt) under high pressure and relatively low temperatures. This process usually occurs in subduction zones or orogenic belts where tectonic plates collide.
Uses & applications
Primarily used as crushed stone for construction, road base, and ornamental landscaping. Historically used for making stone tools (celts and axes) due to its toughness and ability to hold an edge.
Geological facts
The green color is primarily due to the presence of secondary metamorphic minerals like chlorite, epidote, and actinolite which replace the original minerals in the basalt.
Field identification & locations
Identify in the field by its distinct dull green color and high density. It is commonly found in ancient mountain ranges such as the Appalachians, or in volcanic island arc terrains. It will not react with acid and is harder than a steel nail.
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