igneous
Basalt (Greenstone/Water-worn Pebble)
Basalt (containing Chlorite/Epidote)
Hardness: 5-6 (Mohs); Color: Dark olive green to grayish-green; Luster: Dull to waxy; Texture: Fine-grained (aphanitic), smooth due to water erosion; Specific Gravity: 2.8–3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark olive green to grayish-green
- Luster
- Dull to waxy
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark olive green to grayish-green; Luster: Dull to waxy; Texture: Fine-grained (aphanitic), smooth due to water erosion; Specific Gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. The green tint often indicates low-grade metamorphism where minerals like chlorite, epidote, or actinolite have replaced primary minerals.
Uses & applications
Primarily used in construction as crushed stone or aggregate; also used for decorative landscaping, aquariums, and as a natural material for stone massage therapy.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floors. When it turns green through hydrothermal alteration, it is often referred to by geologists as Greenstone.
Field identification & locations
Look for a heavy, fine-grained rock with a dark green hue and absence of visible crystals. Commonly found along riverbeds or coastal beaches where wave action has tumbled the rock into a smooth, oval shape.
