igneous
Greenstone / Basalt
Aphanitic Mafic Igneous Rock (Metabasalt)
Hardness: 6-7 Mohs; Color: dark green to grayish-green; Luster: dull to waxy; Texture: fine-grained (aphanitic); Specific Gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- dark green to grayish-green
- Luster
- dull to waxy
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Physical properties
Hardness: 6-7 Mohs; Color: dark green to grayish-green; Luster: dull to waxy; Texture: fine-grained (aphanitic); Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium and iron-rich lava (basalt) that has undergone low-grade metamorphism, often in marine environments or volcanic arcs.
Uses & applications
Used as aggregate in construction, road base, shoreline protection (riprap), and occasionally for decorative landscaping or lapidary work.
Geological facts
The green color is typically derived from chlorite, actinolite, or epidote minerals formed during the alteration of the original basalt.
Field identification & locations
Commonly found as water-worn cobbles on beaches and in riverbeds. Look for a heavy, dense feel and a characteristic green hue when wet.
