Igneous
Basalt (Vesicular/Scoriaceous)
Extrusive Mafic Volcanic Rock (Primarily Plagioclase Feldspar and Pyroxene)
Hardness: 6 (Mohs scale), Color: Dark grey to black or brownish-black, Luster: Dull/Sub-metallic, Structure: Fine-grained (aphanitic), Specific Gravity: 2.8 - 3.0
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to black or brownish-black, Luster: Dull/Sub-metallic, Structure: Fine-grained (aphanitic), Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. This specimen appears water-worn or weathered, indicating transportation in a river or coastal environment from its volcanic source.
Uses & applications
Used extensively in construction as road base, aggregate for concrete, and railroad ballast. In finer specimens, used for decorative landscaping and stone massage therapy.
Geological facts
Basalt is the most common rock on Earth's surface, making up most of the ocean floor and the lunar maria on the Moon. It contains magnetite, which can make some specimens slightly magnetic.
Field identification & locations
Identify by its heavy weight (density), dark color, and fine-grained texture. It often shows 'vesicles' (small holes from trapped gas bubbles). Commonly found in volcanic regions, oceanic islands, and as river cobbles in drainage basins.
