igneous
Basalt with Vesicles
Aphanitic Mafic Volcanic Rock (Basalt)
Hardness: 6 (Mohs scale); Color: Dark grey to brownish-olive (weathered surface); Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained, invisible to the naked eye); Specific gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to brownish-olive (weathered surface)
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to brownish-olive (weathered surface); Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained, invisible to the naked eye); Specific gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the earth's surface. Small pits (vesicles) occur where gas bubbles were trapped as the lava solidified. Common in regions of oceanic crust and volcanic hotspots.
Uses & applications
Commonly used in construction as aggregate for concrete and asphalt, railroad ballast, and occasionally for high-durability floor tiles or garden landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor; it is also highly common on the Moon and Mars.
Field identification & locations
Identify in the field by its high density relative to other dark stones, its fine-grained texture, and the presence of small rounded pits or gas bubbles. Commonly found on beaches or in riverbeds where it has been smoothed into a cobble/pebble shape.
