igneous
Basalt (Vesicular)
Extrusive Mafic Igneous Rock
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0; Contains gas vesicles (pores).
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0; Contains gas vesicles (pores).
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (magma) exposed at or very near the Earth's surface. Common in volcanic fields and oceanic crust.
Uses & applications
Used primarily in construction (crushed stone, concrete aggregate, asphalt filler), and occasionally as dimension stone or for therapeutic hot stone massages.
Geological facts
Basalt makes up most of the Earth's ocean floor. It is also found extensively on the Moon and Mars, where it forms the dark 'seas' known as lunar maria.
Field identification & locations
Identify in the field by its dark color, high density compared to other local stones, and the presence of tiny holes (vesicles). Found in volcanic regions like Hawaii or the Pacific Northwest.
