igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8–3.0. This specimen appears dark, dense, and fine-grained with some crystalline inclusions.
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8–3.0. This specimen appears dark, dense, and fine-grained with some crystalline inclusions.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. It can range in age from modern volcanic flows to billions of years old.
Uses & applications
Commonly used as crushed stone for road base, concrete aggregate, railroad ballast, and in the manufacturing of stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify in the field by its heavy weight (density), dark color, and lack of visible quartz. It is commonly found in volcanic regions, oceanic islands (like Hawaii), and mid-ocean ridges.
