Igneous
Basalt (Vesicular)
Mafic Volcanic Rock (rich in Magnesium and Iron)
Hardness: 5-6 (Mohs scale); Color: Dark grey, black, or reddish-brown due to oxidation; Luster: Dull/Earthy; Structure: Fine-grained aphanitic with small pits (vesicles); Specific Gravity: 2.8-3.0.
- Hardness
- 5-6 (Mohs scale)
- Color
- Dark grey, black, or reddish-brown due to oxidation
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark grey, black, or reddish-brown due to oxidation; Luster: Dull/Earthy; Structure: Fine-grained aphanitic with small pits (vesicles); Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near a planetary surface. The small holes (vesicles) are created by gas bubbles escaping as the magma cools and solidifies.
Uses & applications
Aggregates for construction, road base, concrete, and as a raw material for 'rock wool' insulation. Larger vesicular pieces are often used in landscaping or as 'lava rocks' for grills.
Geological facts
Basalt is the most common rock type on Earth's crust and makes up most of the ocean floor. It is also highly prevalent on the Moon and Mars.
Field identification & locations
Identify in the field by its high density relative to other small stones, its dark color, and the presence of tiny pits or 'vesicles.' Commonly found in volcanic fields, oceanic islands (like Hawaii), and mid-ocean ridges.
