igneous
Basalt (Vesicular or Weathered)
Aphanitic Mafic Igneous Rock (Basalt)
Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) with small pits or vesicles; Specific Gravity: 2.8-3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) with small pits or vesicles; 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. This specimen appears to have been water-worn or weathered, softening its sharp edges.
Uses & applications
Used extensively in construction as aggregate, for road base, concrete, and railroad ballast. High-quality specimens are used for stone massage or decorative landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identified by its dark color, heavy weight (relative to size), and fine-grained texture. To confirm, look for its magnetic properties (sometimes weak) and lack of visible quartz crystals.
